Basics of fluid Mechamics

Table of contents :
Nomenclature......Page 23
GNU Free Documentation License......Page 33
ADDENDUM: How to use this License for your documents......Page 34
Steven from artofproblemsolving.com......Page 41
Your name here......Page 42
Typo corrections and other "minor" contributions......Page 43
pages 400 size 3.5M......Page 47
pages 151 size 1.3M......Page 48
Internal Viscous Flow......Page 55
Open Channel Flow......Page 56
What is Fluid Mechanics?......Page 58
Brief History......Page 60
Kinds of Fluids......Page 62
Shear Stress......Page 63
General Discussion......Page 66
Non–Newtonian Fluids......Page 68
Estimation of The Viscosity......Page 69
Fluid Density......Page 79
Bulk Modulus......Page 81
Surface Tension......Page 87
Wetting of Surfaces......Page 92
Basic Definitions......Page 102
Thermodynamics First Law......Page 103
Thermodynamics Second Law......Page 104
Kinematics of of Point Body......Page 110
Actual Center of Mass......Page 112
Approximate Center of Area......Page 113
Change of Centroid Location Due to Added/Subtracted Area......Page 114
Change of Mass Centroid Due to Addition or Subtraction of Mass in 3D......Page 120
Moment of Inertia for Mass......Page 123
Moment of Inertia for Area......Page 124
Examples of Moment of Inertia......Page 126
Product of Inertia......Page 130
Newton's Laws of Motion......Page 132
Angular Momentum and Torque......Page 133
Tables of geometries......Page 134
Qualitative questions......Page 138
Constant Density in Gravitational Field......Page 140
Pressure Measurement......Page 144
Varying Density in a Gravity Field......Page 148
The Pressure Effects Due To Temperature Variations......Page 155
Gravity Variations Effects on Pressure and Density......Page 160
Fluid in a Linearly Accelerated System......Page 162
Angular Acceleration Systems: Constant Density......Page 165
Fluid Statics in Geological System......Page 166
Fluid Forces on Straight Surfaces......Page 170
Forces on Curved Surfaces......Page 179
Buoyancy and Stability......Page 186
Stability......Page 196
Surface Tension......Page 223
I Integral Analysis......Page 230
Introduction......Page 232
Control Volume......Page 233
Continuity Equation......Page 234
Constant Density Fluids......Page 236
Reynolds Transport Theorem......Page 243
Examples For Mass Conservation......Page 245
The Details Picture – Velocity Area Relationship......Page 251
More Examples for Mass Conservation......Page 255
Introduction to Continuous......Page 262
External Forces......Page 263
Momentum Equation in Acceleration System......Page 264
Momentum Equation For Steady State and Uniform Flow......Page 265
Momentum Equation Application......Page 269
Momentum for Unsteady State and Uniform Flow......Page 272
Momentum Application to Unsteady State......Page 273
Conservation Moment Of Momentum......Page 283
More Examples on Momentum Conservation......Page 285
Qualitative Questions......Page 287
The First Law of Thermodynamics......Page 290
Limitation of Integral Approach......Page 302
Energy Equation in Steady State......Page 304
Energy Equation in Frictionless Flow and Steady State......Page 305
Energy in Linear Acceleration Coordinate......Page 306
Linear Accelerated System......Page 307
Energy Equation in Rotating Coordinate System......Page 308
Energy Losses in Incompressible Flow......Page 309
Examples of Integral Energy Conservation......Page 311
Qualitative Questions......Page 316
II Differential Analysis......Page 318
Introduction......Page 320
Mass Conservation......Page 321
Mass Conservation Examples......Page 324
Simplified Continuity Equation......Page 326
Generalization of Mathematical Approach for Derivations......Page 331
Examples of Several Quantities......Page 332
Momentum Conservation......Page 334
Derivations of the Momentum Equation......Page 338
Boundary Conditions Categories......Page 349
Examples for Differential Equation (Navier-Stokes)......Page 352
Interfacial Instability......Page 362
Introductory Remarks......Page 366
Brief History......Page 367
Theory Behind Dimensional Analysis......Page 368
Dimensional Parameters Application for Experimental Study......Page 372
The Pendulum Class Problem......Page 373
Buckingham—-Theorem......Page 374
Construction of the Dimensionless Parameters......Page 375
Basic Units Blocks......Page 377
Implementation of Construction of Dimensionless Parameters......Page 380
Similarity and Similitude......Page 389
Nusselt's Technique......Page 393
Summary of Dimensionless Numbers......Page 405
The Significance of these Dimensionless Numbers......Page 409
Relationship Between Dimensionless Numbers......Page 411
Examples for Dimensional Analysis......Page 412
Summary......Page 421
Appendix summary of Dimensionless Form of Navier–Stokes Equations......Page 422
Supplemental Problems......Page 423
Introduction......Page 428
Non–Circular Shape Effect......Page 429
Introduction......Page 432
Colebrook-White equation for Friction Factor,f......Page 441
Entry Problem......Page 442
Non–Circular Shape Effect......Page 447
Losses in Conduits Connections and Other Devices......Page 448
Minor Loss......Page 449
Flow Meters (Flow Measurements)......Page 454
Nozzle Flow Meter......Page 456
Flow Network......Page 457
Series Conduits Systems......Page 458
Parallel Pipe Line Systems......Page 460
Introduction......Page 464
Inviscid Momentum Equations......Page 465
Potential Flow Function......Page 471
Streamline and Stream function......Page 472
Compressible Flow Stream Function......Page 475
The Connection Between the Stream Function and the Potential Function......Page 477
Potential Flow Functions Inventory......Page 481
Flow Around a Circular Cylinder......Page 497
Complex Potential and Complex Velocity......Page 509
Blasius's Integral Laws......Page 513
Forces and Moment Acting on Circular Cylinder.......Page 515
Qualitative questions......Page 516
Additional Example......Page 517
Why Compressible Flow is Important?......Page 524
Introduction......Page 525
Speed of Sound in Ideal and Perfect Gases......Page 527
Speed of Sound in Almost Incompressible Liquid......Page 528
The Dimensional Effect of the Speed of Sound......Page 529
Stagnation State for Ideal Gas Model......Page 531
Isentropic Converging–Diverging Flow in Cross Section......Page 533
The Properties in the Adiabatic Nozzle......Page 534
Isentropic Flow Examples......Page 538
Mass Flow Rate (Number)......Page 541
Isentropic Tables......Page 549
The Impulse Function......Page 551
Normal Shock......Page 553
Solution of the Governing Equations......Page 555
Prandtl's Condition......Page 558
Operating Equations and Analysis......Page 560
The Moving Shocks......Page 562
Shock or Wave Drag Result from a Moving Shock......Page 564
Tables of Normal Shocks, k=1.4 Ideal Gas......Page 566
Isothermal Flow......Page 568
The Control Volume Analysis/Governing equations......Page 569
Dimensionless Representation......Page 570
The Entrance Limitation of Supersonic Branch......Page 574
Supersonic Branch......Page 575
Figures and Tables......Page 576
Isothermal Flow Examples......Page 578
Fanno Flow......Page 583
Introduction......Page 584
Non–Dimensionalization of the Equations......Page 585
The Mechanics and Why the Flow is Choked?......Page 588
The Working Equations......Page 589
Examples of Fanno Flow......Page 593
Working Conditions......Page 599
The Pressure Ratio, .P2 / P1, effects......Page 604
The Practical Questions and Examples of Subsonic branch......Page 613
Subsonic Fanno Flow for Given 4fLD and Pressure Ratio......Page 614
Subsonic Fanno Flow for a Given M1 and Pressure Ratio......Page 618
More Examples of Fanno Flow......Page 620
The Table for Fanno Flow......Page 621
Introduction......Page 623
Governing Equations......Page 624
Rayleigh Flow Tables and Figures......Page 627
Examples For Rayleigh Flow......Page 630
Preface to Oblique Shock......Page 638
Oblique Shock......Page 640
Solution of Mach Angle......Page 642
When No Oblique Shock Exist or the case of D>0......Page 645
Application of Oblique Shock......Page 661
Introduction......Page 673
Geometrical Explanation......Page 675
Alternative Approach to Governing Equations......Page 676
Comparison And Limitations between the Two Approaches......Page 679
d'Alembert's Paradox......Page 680
Flat Body with an Angle of Attack......Page 681
Examples For Prandtl–Meyer Function......Page 682
Combination of the Oblique Shock and Isentropic Expansion......Page 684
Introduction......Page 688
What to Expect From This Chapter......Page 689
Kind of Multi-Phase Flow......Page 690
Classification of Liquid-Liquid Flow Regimes......Page 691
Co–Current Flow......Page 692
Multi–Phase Flow Variables Definitions......Page 696
Multi–Phase Averaged Variables Definitions......Page 697
Homogeneous Models......Page 699
Pressure Loss Components......Page 700
Lockhart Martinelli Model......Page 703
Solid Particles with Heavier Density S>L......Page 704
Solid With Lighter Density S< and With Gravity......Page 706
Counter–Current Flow......Page 708
Horizontal Counter–Current Flow......Page 710
Flooding and Reversal Flow......Page 711
Multi–Phase Conclusion......Page 717
Vectors......Page 718
Vector Algebra......Page 719
Differential Operators of Vectors......Page 721
Differentiation of the Vector Operations......Page 723
First Order Differential Equations......Page 729
Variables Separation or Segregation......Page 730
Non–Linear Equations......Page 732
Second Order Differential Equations......Page 735
Non–Linear Second Order Equations......Page 737
Third Order Differential Equation......Page 740
Forth and Higher Order ODE......Page 742
Partial Differential Equations......Page 744
First-order equations......Page 745
Index......Page 746
Authors Index......Page 748

Citation preview

Basics of Fluid Mechanics

Genick Bar–Meir, Ph. D. 7449 North Washtenaw Ave Chicago, IL 60645 email:genick at potto.org

c 2021, 2020, 2014, 2013, 2011, 2010, 2009, 2008, 2007, and 2006 by Genick Bar-M Copyright See the file copying.fdl or copyright.tex for copying conditions. Version (0.4.0

April 27, 2021)

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iii

“We are like dwarfs sitting on the shoulders of giants”

from The Metalogicon by John in 1159

iv

Contents

Nomenclature GNU Free Documentation License . . . . . . . . . . . . . . . . APPLICABILITY AND DEFINITIONS . . . . . . . . . . . 2. VERBATIM COPYING . . . . . . . . . . . . . . . . . . 3. COPYING IN QUANTITY . . . . . . . . . . . . . . . . 4. MODIFICATIONS . . . . . . . . . . . . . . . . . . . . 5. COMBINING DOCUMENTS . . . . . . . . . . . . . . 6. COLLECTIONS OF DOCUMENTS . . . . . . . . . . . 7. AGGREGATION WITH INDEPENDENT WORKS . . . 8. TRANSLATION . . . . . . . . . . . . . . . . . . . . . 9. TERMINATION . . . . . . . . . . . . . . . . . . . . . 10. FUTURE REVISIONS OF THIS LICENSE . . . . . . . ADDENDUM: How to use this License for your documents How to contribute to this book . . . . . . . . . . . . . . . . . . Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steven from artofproblemsolving.com . . . . . . . . . . . Dan H. Olson . . . . . . . . . . . . . . . . . . . . . . . . Richard Hackbarth . . . . . . . . . . . . . . . . . . . . . . John Herbolenes . . . . . . . . . . . . . . . . . . . . . . . Eliezer Bar-Meir . . . . . . . . . . . . . . . . . . . . . . . Henry Schoumertate . . . . . . . . . . . . . . . . . . . . . Your name here . . . . . . . . . . . . . . . . . . . . . . . Typo corrections and other ”minor” contributions . . . . . Version 0.4 April 6, 2020 . . . . . . . . . . . . . . . . . . . . . pages 749 size 11M . . . . . . . . . . . . . . . . . . . . . Version 0.3.2.0 March 18, 2013 . . . . . . . . . . . . . . . . . . pages 617 size 4.8M . . . . . . . . . . . . . . . . . . . . . Version 0.3.0.5 March 1, 2011 . . . . . . . . . . . . . . . . . . pages 400 size 3.5M . . . . . . . . . . . . . . . . . . . . . Version 0.1.8 August 6, 2008 . . . . . . . . . . . . . . . . . . . pages 189 size 2.6M . . . . . . . . . . . . . . . . . . . . . Version 0.1 April 22, 2008 . . . . . . . . . . . . . . . . . . . . . pages 151 size 1.3M . . . . . . . . . . . . . . . . . . . . . Properties . . . . . . . . . . . . . . . . . . . . . . . . . .

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CONTENTS Turbulence . . . . . . Inviscid Flow . . . . . Machinery . . . . . . Internal Viscous Flow Open Channel Flow .

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2 Review of Thermodynamics 2.1 Introductory Remarks . . . . . . . . 2.2 Basic Definitions . . . . . . . . . . 2.3 Thermodynamics First Law . . . . . 2.4 Thermodynamics Second Law . . .

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1 Introduction to Fluid Mechanics 1.1 What is Fluid Mechanics? . . . . 1.2 Brief History . . . . . . . . . . . 1.3 Kinds of Fluids . . . . . . . . . . . 1.4 Shear Stress . . . . . . . . . . . . 1.5 Viscosity . . . . . . . . . . . . . . 1.5.1 General Discussion . . . . 1.5.2 Non–Newtonian Fluids . . 1.5.3 Kinematic Viscosity . . . . 1.5.4 Estimation of The Viscosity 1.6 Fluid Properties . . . . . . . . . . 1.6.1 Fluid Density . . . . . . . 1.6.2 Bulk Modulus . . . . . . . 1.7 Surface Tension . . . . . . . . . . 1.7.1 Wetting of Surfaces . . . .

3 Review of Mechanics 3.1 Introductory Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Kinematics of of Point Body . . . . . . . . . . . . . . . . . . . . . . . 3.3 Center of Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Actual Center of Mass . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Approximate Center of Area . . . . . . . . . . . . . . . . . . . 3.3.3 Change of Centroid Location Due to Added/Subtracted Area . . 3.3.4 Change of Mass Centroid Due to Addition or Subtraction of Mass in 3D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Moment of Inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Moment of Inertia for Mass . . . . . . . . . . . . . . . . . . . . 3.4.2 Moment of Inertia for Area . . . . . . . . . . . . . . . . . . . 3.4.3 Examples of Moment of Inertia . . . . . . . . . . . . . . . . . . 3.4.4 Product of Inertia . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.5 Principal Axes of Inertia . . . . . . . . . . . . . . . . . . . . . . 3.5 Newton’s Laws of Motion . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Angular Momentum and Torque . . . . . . . . . . . . . . . . . . . . .

53 53 53 55 55 56 57 63 66 66 67 69 73 75 75 76

CONTENTS 3.6.1

vii Tables of geometries . . . . . . . . . . . . . . . . . . . . . . .

4 Fluids Statics 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 The Hydrostatic Equation . . . . . . . . . . . . . . . . . . 4.3 Pressure and Density in a Gravitational Field . . . . . . . . 4.3.1 Constant Density in Gravitational Field . . . . . . . 4.3.2 Pressure Measurement . . . . . . . . . . . . . . . . 4.3.3 Varying Density in a Gravity Field . . . . . . . . . . 4.3.4 The Pressure Effects Due To Temperature Variations 4.3.5 Gravity Variations Effects on Pressure and Density . 4.3.6 Liquid Phase . . . . . . . . . . . . . . . . . . . . . 4.4 Fluid in a Accelerated System . . . . . . . . . . . . . . . . 4.4.1 Fluid in a Linearly Accelerated System . . . . . . . 4.4.2 Angular Acceleration Systems: Constant Density . . 4.4.3 Fluid Statics in Geological System . . . . . . . . . . 4.5 Fluid Forces on Surfaces . . . . . . . . . . . . . . . . . . . 4.5.1 Fluid Forces on Straight Surfaces . . . . . . . . . . 4.5.2 Forces on Curved Surfaces . . . . . . . . . . . . . . 4.6 Buoyancy and Stability . . . . . . . . . . . . . . . . . . . . 4.6.1 Stability . . . . . . . . . . . . . . . . . . . . . . . . 4.0.1 Surface Tension . . . . . . . . . . . . . . . . . . . . 4.1 Rayleigh–Taylor Instability . . . . . . . . . . . . . . . . . . 4.2 Qualitative questions . . . . . . . . . . . . . . . . . . . . .

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Integral Analysis

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5 Mass Conservation 5.1 Introduction . . . . . . . . . . . . . . . . . . . . 5.2 Control Volume . . . . . . . . . . . . . . . . . . 5.3 Continuity Equation . . . . . . . . . . . . . . . 5.3.1 Non Deformable Control Volume . . . . 5.3.2 Constant Density Fluids . . . . . . . . . 5.4 Reynolds Transport Theorem . . . . . . . . . . . 5.5 Examples For Mass Conservation . . . . . . . . 5.6 The Details Picture – Velocity Area Relationship 5.7 More Examples for Mass Conservation . . . . . . 6 Momentum Conservation 6.1 Momentum Governing Equation . . . . . . 6.1.1 Introduction to Continuous . . . . 6.1.2 External Forces . . . . . . . . . . . 6.1.3 Momentum Governing Equation . . 6.1.4 Momentum Equation in Acceleration

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viii

CONTENTS 6.2

6.3 6.4

6.1.5 Momentum Equation For Steady State and Uniform Flow Momentum Equation Application . . . . . . . . . . . . . . . . . 6.2.1 Momentum for Unsteady State and Uniform Flow . . . . 6.2.2 Momentum Application to Unsteady State . . . . . . . . Conservation Moment Of Momentum . . . . . . . . . . . . . . . More Examples on Momentum Conservation . . . . . . . . . . . 6.4.1 Qualitative Questions . . . . . . . . . . . . . . . . . . . .

7 Energy Conservation 7.1 The First Law of Thermodynamics . . . . . . . . . . . . . . . 7.2 Limitation of Integral Approach . . . . . . . . . . . . . . . . 7.3 Approximation of Energy Equation . . . . . . . . . . . . . . . 7.3.1 Energy Equation in Steady State . . . . . . . . . . . 7.3.2 Energy Equation in Frictionless Flow and Steady State 7.4 Energy Equation in Accelerated System . . . . . . . . . . . . 7.4.1 Energy in Linear Acceleration Coordinate . . . . . . . 7.4.2 Linear Accelerated System . . . . . . . . . . . . . . . 7.4.3 Energy Equation in Rotating Coordinate System . . . 7.4.4 Simplified Energy Equation in Accelerated Coordinate 7.4.5 Energy Losses in Incompressible Flow . . . . . . . . . 7.5 Examples of Integral Energy Conservation . . . . . . . . . . . 7.6 Qualitative Questions . . . . . . . . . . . . . . . . . . . . . .

II

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Differential Analysis

8 Differential Analysis 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Mass Conservation . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Mass Conservation Examples . . . . . . . . . . . . . . . 8.2.2 Simplified Continuity Equation . . . . . . . . . . . . . . 8.3 Conservation of General Quantity . . . . . . . . . . . . . . . . 8.3.1 Generalization of Mathematical Approach for Derivations 8.3.2 Examples of Several Quantities . . . . . . . . . . . . . 8.4 Momentum Conservation . . . . . . . . . . . . . . . . . . . . . 8.5 Derivations of the Momentum Equation . . . . . . . . . . . . . 8.6 Boundary Conditions and Driving Forces . . . . . . . . . . . . 8.6.1 Boundary Conditions Categories . . . . . . . . . . . . . 8.7 Examples for Differential Equation (Navier-Stokes) . . . . . . . 8.7.1 Interfacial Instability . . . . . . . . . . . . . . . . . . .

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CONTENTS

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9 Dimensional Analysis 9.1 Introductory Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.1 Brief History . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.2 Theory Behind Dimensional Analysis . . . . . . . . . . . . . 9.1.3 Dimensional Parameters Application for Experimental Study . 9.1.4 The Pendulum Class Problem . . . . . . . . . . . . . . . . . 9.2 Buckingham–π–Theorem . . . . . . . . . . . . . . . . . . . . . . . . 9.2.1 Construction of the Dimensionless Parameters . . . . . . . . 9.2.2 Basic Units Blocks . . . . . . . . . . . . . . . . . . . . . . . 9.2.3 Implementation of Construction of Dimensionless Parameters 9.2.4 Similarity and Similitude . . . . . . . . . . . . . . . . . . . . 9.3 Nusselt’s Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Summary of Dimensionless Numbers . . . . . . . . . . . . . . . . . . 9.4.1 The Significance of these Dimensionless Numbers . . . . . . 9.4.2 Relationship Between Dimensionless Numbers . . . . . . . . 9.4.3 Examples for Dimensional Analysis . . . . . . . . . . . . . . 9.5 Abuse of Dimensional Analysis . . . . . . . . . . . . . . . . . . . . . 9.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Appendix summary of Dimensionless Form of Navier–Stokes Equations 9.8 Supplemental Problems . . . . . . . . . . . . . . . . . . . . . . . . .

309 309 310 311 315 316 317 318 320 323 332 336 348 352 354 355 364 364 365 . 366

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10 External Flow 371 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 10.2 Boundary Layer Theory . . . . . . . . . . . . . . . . . . . . . . . . . . 372 10.2.1 Non–Circular Shape Effect . . . . . . . . . . . . . . . . . . . . 372 11 Internal Flow 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Colebrook-White equation for Friction Factor,f 11.2 Entry Problem . . . . . . . . . . . . . . . . . . . . . 11.2.1 Non–Circular Shape Effect . . . . . . . . . . . 11.3 Losses in Conduits Connections and Other Devices . . 11.3.1 Minor Loss . . . . . . . . . . . . . . . . . . . . 11.3.2 Flow Meters (Flow Measurements) . . . . . . . 11.3.3 Nozzle Flow Meter . . . . . . . . . . . . . . . 11.4 Flow Network . . . . . . . . . . . . . . . . . . . . . . 11.4.1 Series Conduits Systems . . . . . . . . . . . . 11.4.2 Parallel Pipe Line Systems . . . . . . . . . . .

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375 375 384 385 390 391 392 397 399 400 401 403

12 Potential Flow 12.1 Introduction . . . . . . . . . . . . . . . . . 12.1.1 Inviscid Momentum Equations . . . 12.2 Potential Flow Function . . . . . . . . . . . 12.2.1 Streamline and Stream function . . 12.2.2 Compressible Flow Stream Function

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407 407 408 414 415 418

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CONTENTS

12.3 12.4 12.5

12.6 12.7 12.8

12.2.3 The Connection Between the Stream Function and the Potential Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potential Flow Functions Inventory . . . . . . . . . . . . . . . . . . . 12.3.1 Flow Around a Circular Cylinder . . . . . . . . . . . . . . . . . Complex Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.1 Complex Potential and Complex Velocity . . . . . . . . . . . . Blasius’s Integral Laws . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5.1 Forces and Moment Acting on Circular Cylinder. . . . . . . . . 12.5.2 Conformal Transformation or Mapping . . . . . . . . . . . . . . Unsteady State Bernoulli in Accelerated Coordinates . . . . . . . . . . Qualitative questions . . . . . . . . . . . . . . . . . . . . . . . . . . . Additional Example . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 Compressible Flow One Dimensional 13.1 What is Compressible Flow? . . . . . . . . . . . . . . . . . . 13.2 Why Compressible Flow is Important? . . . . . . . . . . . . . 13.3 Speed of Sound . . . . . . . . . . . . . . . . . . . . . . . . . 13.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 13.3.2 Speed of Sound in Ideal and Perfect Gases . . . . . . 13.3.3 Speed of Sound in Almost Incompressible Liquid . . . 13.3.4 Speed of Sound in Solids . . . . . . . . . . . . . . . . 13.3.5 The Dimensional Effect of the Speed of Sound . . . . 13.4 Isentropic Flow . . . . . . . . . . . . . . . . . . . . . . . . . 13.4.1 Stagnation State for Ideal Gas Model . . . . . . . . . 13.4.2 Isentropic Converging–Diverging Flow in Cross Section 13.4.3 The Properties in the Adiabatic Nozzle . . . . . . . . 13.4.4 Isentropic Flow Examples . . . . . . . . . . . . . . . 13.4.5 Mass Flow Rate (Number) . . . . . . . . . . . . . . . 13.4.6 Isentropic Tables . . . . . . . . . . . . . . . . . . . . 13.4.7 The Impulse Function . . . . . . . . . . . . . . . . . 13.5 Normal Shock . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5.1 Solution of the Governing Equations . . . . . . . . . . 13.5.2 Prandtl’s Condition . . . . . . . . . . . . . . . . . . . 13.5.3 Operating Equations and Analysis . . . . . . . . . . . 13.5.4 The Moving Shocks . . . . . . . . . . . . . . . . . . 13.5.5 Shock or Wave Drag Result from a Moving Shock . . 13.5.6 Qualitative questions . . . . . . . . . . . . . . . . . . 13.5.7 Tables of Normal Shocks, k = 1.4 Ideal Gas . . . . . 13.6 Isothermal Flow . . . . . . . . . . . . . . . . . . . . . . . . . 13.6.1 The Control Volume Analysis/Governing equations . . 13.6.2 Dimensionless Representation . . . . . . . . . . . . . 13.6.3 The Entrance Limitation of Supersonic Branch . . . . 13.6.4 Supersonic Branch . . . . . . . . . . . . . . . . . . . 13.6.5 Figures and Tables . . . . . . . . . . . . . . . . . . .

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420 424 440 452 452 456 458 459 459 459 460 467 467 467 468 468 470 471 472 472 474 474 476 477 481 484 492 494 496 498 501 503 505 507 509 509 511 512 513 517 518 519

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xi

13.6.6 Isothermal Flow Examples . . . . . . . . . . . . . . . . . 13.7 Fanno Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 13.7.2 Non–Dimensionalization of the Equations . . . . . . . . . 13.7.3 The Mechanics and Why the Flow is Choked? . . . . . . 13.7.4 The Working Equations . . . . . . . . . . . . . . . . . . 13.7.5 Examples of Fanno Flow . . . . . . . . . . . . . . . . . . 13.7.6 Working Conditions . . . . . . . . . . . . . . . . . . . . . 13.7.7 The Pressure Ratio, P2 / P1 , effects . . . . . . . . . . . . 13.7.8 Practical Examples for Subsonic Flow . . . . . . . . . . . 13.7.9 The Practical Questions and Examples of Subsonic branch fL 13.7.10 Subsonic Fanno Flow for Given 4 D and Pressure Ratio . 13.7.11 Subsonic Fanno Flow for a Given M1 and Pressure Ratio . 13.7.12 More Examples of Fanno Flow . . . . . . . . . . . . . . . 13.8 The Table for Fanno Flow . . . . . . . . . . . . . . . . . . . . . 13.9 Rayleigh Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 13.9.2 Governing Equations . . . . . . . . . . . . . . . . . . . . 13.9.3 Rayleigh Flow Tables and Figures . . . . . . . . . . . . . 13.9.4 Examples For Rayleigh Flow . . . . . . . . . . . . . . . .

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521 526 527 528 531 532 536 542 547 556 556 557 561 563 564 566 566 567 570 573

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581 581 581 583 585 588 604 616 616 618 619 622 623 623 623 624 625 627

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631 631 632 632 633

14 Compressible Flow 2–Dimensional 14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.1.1 Preface to Oblique Shock . . . . . . . . . . . . . . . . . 14.2 Oblique Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.2.1 Solution of Mach Angle . . . . . . . . . . . . . . . . . . 14.2.2 When No Oblique Shock Exist or the case of D > 0 . . . 14.2.3 Application of Oblique Shock . . . . . . . . . . . . . . . 14.3 Prandtl-Meyer Function . . . . . . . . . . . . . . . . . . . . . . 14.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 14.3.2 Geometrical Explanation . . . . . . . . . . . . . . . . . . 14.3.3 Alternative Approach to Governing Equations . . . . . . . 14.3.4 Comparison And Limitations between the Two Approaches 14.4 The Maximum Turning Angle . . . . . . . . . . . . . . . . . . . 14.5 The Working Equations for the Prandtl-Meyer Function . . . . . 14.6 d’Alembert’s Paradox . . . . . . . . . . . . . . . . . . . . . . . . 14.7 Flat Body with an Angle of Attack . . . . . . . . . . . . . . . . 14.8 Examples For Prandtl–Meyer Function . . . . . . . . . . . . . . . 14.9 Combination of the Oblique Shock and Isentropic Expansion . . .

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15 Multi–Phase Flow 15.1 Introduction . . . . . . . . . . . . . 15.2 History . . . . . . . . . . . . . . . 15.3 What to Expect From This Chapter 15.4 Kind of Multi-Phase Flow . . . . .

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xii

CONTENTS 15.5 Classification of Liquid-Liquid Flow Regimes . . . . . . . . 15.5.1 Co–Current Flow . . . . . . . . . . . . . . . . . . . 15.6 Multi–Phase Flow Variables Definitions . . . . . . . . . . . 15.6.1 Multi–Phase Averaged Variables Definitions . . . . . 15.7 Homogeneous Models . . . . . . . . . . . . . . . . . . . . 15.7.1 Pressure Loss Components . . . . . . . . . . . . . . 15.7.2 Lockhart Martinelli Model . . . . . . . . . . . . . . 15.8 Solid–Liquid Flow . . . . . . . . . . . . . . . . . . . . . . . 15.8.1 Solid Particles with Heavier Density ρS > ρL . . . . 15.8.2 Solid With Lighter Density ρS < ρ and With Gravity 15.9 Counter–Current Flow . . . . . . . . . . . . . . . . . . . . 15.9.1 Horizontal Counter–Current Flow . . . . . . . . . . 15.9.2 Flooding and Reversal Flow . . . . . . . . . . . . . 15.10Multi–Phase Conclusion . . . . . . . . . . . . . . . . . . . .

A Mathematics For Fluid Mechanics A.1 Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . A.1.1 Vector Algebra . . . . . . . . . . . . . . . . . . A.1.2 Differential Operators of Vectors . . . . . . . . A.1.3 Differentiation of the Vector Operations . . . . A.2 Ordinary Differential Equations (ODE) . . . . . . . . . A.2.1 First Order Differential Equations . . . . . . . . A.2.2 Variables Separation or Segregation . . . . . . A.2.3 Non–Linear Equations . . . . . . . . . . . . . . A.2.4 Second Order Differential Equations . . . . . . A.2.5 Non–Linear Second Order Equations . . . . . . A.2.6 Third Order Differential Equation . . . . . . . A.2.7 Forth and Higher Order ODE . . . . . . . . . . A.2.8 A general Form of the Homogeneous Equation A.3 Partial Differential Equations . . . . . . . . . . . . . . A.3.1 First-order equations . . . . . . . . . . . . . . A.4 Trigonometry . . . . . . . . . . . . . . . . . . . . . .

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634 635 639 640 642 643 646 647 647 649 651 653 654 660

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661 661 662 664 666 672 672 673 675 678 680 683 685 687 687 688 689

Index 691 Subjects Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691 Authors Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697

List of Figures

1.1 1.2 1.3 1.4 1.5 1.6

1.7 1.8 1.9 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25

Diagram to explain fluid mechanics branches . . . . . . . Density as a function of the size of sample . . . . . . . . Schematics to describe the shear stress in fluid mechanics The deformation of fluid due to shear stress . . . . . . . The difference of power fluids . . . . . . . . . . . . . . . Nitrogen (left) and Argon (right) viscosity . . . . . . . . (a) Nitrogen viscosity . . . . . . . . . . . . . . . . . . (b) Argon viscosity . . . . . . . . . . . . . . . . . . . The shear stress as a function of the shear rate . . . . . Air viscosity as a function of the temperature . . . . . . Water viscosity as a function temperature. . . . . . . . . Liquid metals viscosity as a function of the temperature . Reduced viscosity as function of the reduced temperature Reduced viscosity as function of the reduced temperature Concentrating cylinders with the rotating inner cylinder . Rotating disc in a steady state . . . . . . . . . . . . . . Water density as a function of temperature . . . . . . . Two liquid layers under pressure . . . . . . . . . . . . . Surface tension control volume analysis . . . . . . . . . Surface tension erroneous explanation . . . . . . . . . . Glass tube inserted into mercury . . . . . . . . . . . . . Capillary rise between two plates . . . . . . . . . . . . . Forces in Contact angle . . . . . . . . . . . . . . . . . . Description of wetting and non–wetting fluids . . . . . . Description of the liquid surface . . . . . . . . . . . . . The raising height as a function of the radii . . . . . . . The raising height as a function of the radius . . . . . .

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2 6 7 8 10 10 10 10 11 12 12 14 17 18 20 21 23 27 31 31 33 34 35 36 38 40 41

3.1 3.2 3.3 3.4 3.5 3.6 3.7

Description of the extinguish nozzle . . . . . . . . Description of how the center of mass is calculated Thin body center of mass/area schematic . . . . . Solid body with removed and added area . . . . . . Subtraction circle for a large circle . . . . . . . . . Trapezoid from rectangle . . . . . . . . . . . . . . Mass Center Moving to New Location center . . .

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54 55 56 57 58 58 59

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xiv

LIST OF FIGURES 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21

Movement of area Center to new location . . . . . . . . . . . . . Triangle turns to trapezoid . . . . . . . . . . . . . . . . . . . . . The centroid of the small triangle . . . . . . . . . . . . . . . . . . Mass centroid of cylinder wedge . . . . . . . . . . . . . . . . . . The schematic that explains the summation of moment of inertia . The schematic to explain the summation of moment of inertia . . Cylinder with an element for calculation moment of inertia . . . . Description of rectangular in x–y plane. . . . . . . . . . . . . . . A square element for the calculations of inertia. . . . . . . . . . . The ratio of the moment of inertia 2D to 3D. . . . . . . . . . . . Moment of inertia for rectangular . . . . . . . . . . . . . . . . . . Description of parabola - moment of inertia and center of area . . Triangle for example 3.13 . . . . . . . . . . . . . . . . . . . . . . Product of inertia for triangle . . . . . . . . . . . . . . . . . . . .

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60 61 61 64 68 69 69 70 70 71 71 72 73 74

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.17 4.16 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29

Description of a fluid element in accelerated system. . . . . . Pressure lines in a static constant density fluid . . . . . . . . . A schematic to explain the atmospheric pressure measurement The effective gravity is for accelerated cart . . . . . . . . . . . Tank and the effects different liquids . . . . . . . . . . . . . Schematic of gas measurement utilizing the “U” tube . . . . . Schematic of sensitive measurement device . . . . . . . . . . . Inclined manometer . . . . . . . . . . . . . . . . . . . . . . . Inverted manometer . . . . . . . . . . . . . . . . . . . . . . Hydrostatic pressure under a compressible liquid phase . . . . Two adjoin layers for stability analysis . . . . . . . . . . . . . The varying gravity effects on density and pressure . . . . . . The effective gravity is for accelerated cart . . . . . . . . . . . A cart slide on inclined plane . . . . . . . . . . . . . . . . . . Forces diagram of cart sliding on inclined plane . . . . . . . . Schematic angular angle to explain example 4.10 . . . . . . . Schematic to explain the angular angle . . . . . . . . . . . . . Earth layers not to scale . . . . . . . . . . . . . . . . . . . . . Illustration of the effects of the different radii . . . . . . . . . Rectangular area under pressure . . . . . . . . . . . . . . . . Schematic of submerged area . . . . . . . . . . . . . . . . . . The general forces acting on submerged area . . . . . . . . . . The general forces acting on non symmetrical straight area . . The general forces acting on a non symmetrical straight area . The effects of multi layers density on static forces . . . . . . . The forces on curved area . . . . . . . . . . . . . . . . . . . . Schematic of Net Force on floating body . . . . . . . . . . . . Circular shape Dam . . . . . . . . . . . . . . . . . . . . . . . Area above the dam arc subtract triangle . . . . . . . . . . .

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81 83 84 85 86 88 89 90 91 94 101 103 106 107 107 108 108 110 111 113 115 115 117 118 121 122 123 124 124

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LIST OF FIGURES

xv

4.30 4.31 4.32 4.33 4.34 4.35 4.36 4.37 4.38 4.39 4.40 4.41 4.42 4.43 4.44 4.45 4.46 4.47 4.48 4.49 4.50 4.51 4.52 4.53 4.54 4.55 4.56 4.57 4.58 4.59 4.60 4.61

Area above the dam arc calculation for the center . . . . . . . . . Moment on arc element around Point “O” . . . . . . . . . . . . . Polynomial shape dam description . . . . . . . . . . . . . . . . . The difference between the slop and the direction angle . . . . . . Schematic of Immersed Cylinder . . . . . . . . . . . . . . . . . . The floating forces on Immersed Cylinder . . . . . . . . . . . . . Schematic of a thin wall floating body . . . . . . . . . . . . . . . Schematic of floating bodies . . . . . . . . . . . . . . . . . . . . Center of mass arbitrary floating body . . . . . . . . . . . . . . . Bouguer Showing Metacenter . . . . . . . . . . . . . . . . . . . . Typical rotation of ship/floating body . . . . . . . . . . . . . . . Schematic of Cubic showing the body center and center lift . . . . The Change Of Angle Due Tilting . . . . . . . . . . . . . . . . . Cubic on the side (45◦ ) stability analysis . . . . . . . . . . . . . . Arbitrary body tilted with θ Buoyancy Center move α . . . . . . . Rectangular floating in a liquid . . . . . . . . . . . . . . . . . . . Extruded rectangular body stability analysis . . . . . . . . . . . . Floating upside down triangle in liquid . . . . . . . . . . . . . . . Cylinder in upright position stability . . . . . . . . . . . . . . . . Cone stability calculations . . . . . . . . . . . . . . . . . . . . . . T shape floating to demonstrate the 3D. The rolling creates yaw . Stability analysis of floating body . . . . . . . . . . . . . . . . . . Cubic body dimensions for stability analysis . . . . . . . . . . . . Stability of two triangles put tougher . . . . . . . . . . . . . . . . The effects of liquid movement on the GM . . . . . . . . . . . . Measurement of GM of floating body . . . . . . . . . . . . . . . . Calculations of GM for abrupt shape body . . . . . . . . . . . . . A heavy needle is floating on a liquid. . . . . . . . . . . . . . . . Description of depression to explain the Rayleigh–Taylor instability Description of depression to explain the instability . . . . . . . . . The cross section of the interface for max liquid. . . . . . . . . . Three liquids layers under rotation . . . . . . . . . . . . . . . . .

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125 126 127 128 129 130 131 139 140 140 141 142 143 143 144 145 147 147 149 150 153 154 157 158 159 160 162 166 167 169 170 171

5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11

Control volume and system in motion . . . . . . . . . . Piston control volume . . . . . . . . . . . . . . . . . . . Schematics of velocities at the interface . . . . . . . . . Schematics of flow in a pipe with varying density . . . . Filling of the bucket and choices of the control volumes . Height of the liquid for example 5.4 . . . . . . . . . . . Boundary Layer control mass . . . . . . . . . . . . . . . Control volume usage to calculate local averaged velocity Control volume and system in the motion . . . . . . . . Circular cross section for finding Ux . . . . . . . . . . . Velocity for a circular shape . . . . . . . . . . . . . . . .

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175 176 177 178 181 184 189 194 195 196 197

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xvi

LIST OF FIGURES 5.12 5.13 5.14 5.15

Boat for example 5.14 . . . . . Water Jet Pump . . . . . . . . . Schematic for a centrifugal pump schematic of centrifugal pump .

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198 201 202 202

6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14

The explanation for the direction relative to surface . . . . . . . Schematics of area impinged by a jet . . . . . . . . . . . . . . . Nozzle schematic for forces calculations . . . . . . . . . . . . . Propeller schematic to explain the change of momentum . . . . Toy Sled pushed by the liquid jet . . . . . . . . . . . . . . . . . A rocket with a moving control volume . . . . . . . . . . . . . . Schematic of a tank seating on wheels . . . . . . . . . . . . . . A new control volume to find the velocity in discharge tank . . . A large Ring pushing liquid inside cylinder assembly . . . . . . . Jump in the velocity across the control volume boundary . . . . The impeller of the centrifugal pump and the velocities diagram Nozzle schematics water rocket . . . . . . . . . . . . . . . . . . Flow out of un symmetrical tank . . . . . . . . . . . . . . . . . The explanation for the direction relative to surface . . . . . . .

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206 209 211 213 214 215 217 218 222 224 227 228 231 232

7.1 7.2 7.3 7.4

The work on the control volume . . . . . . . . . . Discharge from a Large Container . . . . . . . . . Kinetic Energy and Averaged Velocity . . . . . . . Typical resistance for selected outlet configuration . (a) Projecting pipe K= 1 . . . . . . . . . . . . . (b) Sharp edge pipe connection K=0.5 . . . . . . (c) Rounded inlet pipe K=0.04 . . . . . . . . . . Flow in an oscillating manometer . . . . . . . . . . A long pipe exposed to a sudden pressure difference Liquid exiting a large tank trough a long tube . . . Tank control volume for Example 7.2 . . . . . . .

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234 236 238 246 246 246 246 246 254 256 257

The mass balance on the infinitesimal control volume . . . . . . . . The mass conservation in cylindrical coordinates . . . . . . . . . . . Mass flow due to temperature difference . . . . . . . . . . . . . . . Mass flow in coating process . . . . . . . . . . . . . . . . . . . . . Stress diagram on a tetrahedron shape . . . . . . . . . . . . . . . . Diagram to analysis the shear stress tensor . . . . . . . . . . . . . . The shear stress creating torque . . . . . . . . . . . . . . . . . . . The shear stress at different surfaces . . . . . . . . . . . . . . . . . Control volume at t and t + dt under continuous angle deformation Shear stress at two coordinates in 45◦ orientations . . . . . . . . . . Different rectangles deformations . . . . . . . . . . . . . . . . . . . (a) Deformations of the isosceles triangular . . . . . . . . . . . . (b) Deformations of the straight angle triangle . . . . . . . . . .

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264 266 268 270 278 279 280 281 283 284 286 286 286

7.5 7.6 7.7 7.8 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11

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LIST OF FIGURES

xvii

8.12 8.13 8.14 8.15 8.16 8.17 8.18 8.19 8.20 8.21

Linear strain of the element . . . . . . . . . . . . . 1–Dimensional free surface . . . . . . . . . . . . . Flow driven by surface tension . . . . . . . . . . . Flow in kendle with a surfece tension gradient . . . Flow between two plates when the top moving . . . One dimensional flow with shear between plates . . The control volume of liquid element in “short cut” Flow of Liquid between concentric cylinders . . . . Mass flow due to temperature difference . . . . . . Liquid flow due to gravity . . . . . . . . . . . . . .

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287 292 295 295 296 297 298 300 303 305

9.1 9.2 9.3 9.4 9.5 9.6

Fitting rod into a hole . . . . . . . . . Pendulum for dimensional analysis . . Resistance of infinite cylinder . . . . . Oscillating Von Karman Vortex Street Description of the boat crossing river . Floating body showing alpha . . . . .

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315 316 323 351 360 363

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10.1 Boundary layer schamatics . . . . . . . . . . . . . . . . . . . . . . . . 371 10.2 General discribtion of boundry layer . . . . . . . . . . . . . . . . . . . 373 11.1 11.2 11.3 11.5

A simple Entry length into a pipe under laminar flow . . . . . . Fully developed and steady state flow in pipe . . . . . . . . . . Moody Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . Transition between the turbulent to laminar flow . . . . . . . . (a) Velocity Regions in pipes . . . . . . . . . . . . . . . . . . (b) Roughness parameter . . . . . . . . . . . . . . . . . . . . 11.6 Laminar Boundary Layer creating the Entry Length . . . . . . . 11.7 Boundary Layer creating the Entry Length for turbulent flow . . 11.8 The entry loss into pipe based on the geometrical configurations (a) Pipe with an inward connection . . . . . . . . . . . . . . (b) Pipe with a squared connection . . . . . . . . . . . . . . . (c) Pipe with a chamfered connection . . . . . . . . . . . . . (d) Pipe with a round connection . . . . . . . . . . . . . . . (e) Pipe with a round connection . . . . . . . . . . . . . . . 11.9 Abrupt expansion for turbulent flow . . . . . . . . . . . . . . . 11.10 Transition from small to large diameter . . . . . . . . . . . . . (a) Sudden expansion loss coefficient . . . . . . . . . . . . . . (b) Relationship of gradual expansion to abrupt expansion . . 11.11The resistance in 90◦ bend with relative roughness . . . . . . . 11.12Various connection for conduits network . . . . . . . . . . . . . (a) Tee connection (inline) . . . . . . . . . . . . . . . . . . . (b) Y connection. . . . . . . . . . . . . . . . . . . . . . . . . (c) Bend connection . . . . . . . . . . . . . . . . . . . . . . 11.13Various valves “switch” for conduits network . . . . . . . . . . .

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375 377 378 383 383 383 385 386 387 387 387 387 387 387 388 390 390 390 393 393 393 393 393 394

xviii

LIST OF FIGURES

(a) Globe value . . . . . . . . . . . . . . . . . . . . . . . (b) Angle valve . . . . . . . . . . . . . . . . . . . . . . . (c) Gate valve. . . . . . . . . . . . . . . . . . . . . . . . (d) Butterfly Valve. . . . . . . . . . . . . . . . . . . . . . (e) Ball Valve. . . . . . . . . . . . . . . . . . . . . . . . . 11.14Coupling connection in a network . . . . . . . . . . . . . . . 11.15Orifice Plate is used measurement flow rate . . . . . . . . . 11.16The resistance due to the Orifice data . . . . . . . . . . . . 11.17The resistance due to Orifice in high Reynolds number . . . 11.18Nozzle flow meter . . . . . . . . . . . . . . . . . . . . . . . 11.19Venturi meter schematic shown the head in different location 11.20 Two different categories of pipe network . . . . . . . . . . . (a) Parallel connections . . . . . . . . . . . . . . . . . . (b) Series Connections . . . . . . . . . . . . . . . . . . .

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394 394 394 394 394 394 397 398 399 399 399 401 401 401

12.1 Streamlines to explain stream function . . . . . . . . . . . . . . . . . . 416 12.2 Streamlines with different different element direction to explain stream function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 (a) Streamlines with element in X direction to explain stream function 417 (b) Streamlines with element in the Y direction to explain stream function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 12.3 Constant Stream lines and Constant Potential lines . . . . . . . . . . . 421 12.4 Stream lines and potential lines are drawn as drawn for two dimensional flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 12.5 Stream lines and potential lines for Example 12.3 . . . . . . . . . . . . 423 12.7 Streamlines and Potential lines due to Source or sink . . . . . . . . . . 425 12.6 Uniform Flow Streamlines and Potential Lines . . . . . . . . . . . . . . 426 12.8 Vortex free flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 12.9 Circulation path to illustrate varies calculations . . . . . . . . . . . . . 429 12.10Combination of the Source and Sink . . . . . . . . . . . . . . . . . . . 432 12.11Stream and Potential line for a source and sink . . . . . . . . . . . . . 434 12.12Stream and potential lines for doublet . . . . . . . . . . . . . . . . . . 439 12.13Stream function of uniform flow plus doublet . . . . . . . . . . . . . . 442 12.14Source in the Uniform Flow . . . . . . . . . . . . . . . . . . . . . . . . 443 12.15Velocity field around a doublet in uniform velocity . . . . . . . . . . . . 444 12.16Doublet in a uniform flow with Vortex in various conditions. . . . . . . 449 (a) Streamlines of doublet in uniform field with Vortex . . . . . . . . 449 (b) Boundary case for streamlines of doublet in uniform field with Vortex449 12.17Schematic to explain Magnus’s effect . . . . . . . . . . . . . . . . . . . 451 12.18Wing in a typical uniform flow . . . . . . . . . . . . . . . . . . . . . . 451 12.19Contour of two dimensional body with control volume . . . . . . . . . . 456 12.20Uniform flow with a sink . . . . . . . . . . . . . . . . . . . . . . . . . 462 13.1 A very slow moving piston in a still gas . . . . . . . . . . . . . . . . . . 468 13.2 Stationary sound wave and gas moves relative to the pulse . . . . . . . 468

LIST OF FIGURES

xix

13.3 Moving object at three relative velocities . . . . . . . . . . . . . . . . 473 (a) Object travels at 0.005 of the speed of sound . . . . . . . . . . . 473 (b) Object travels at 0.05 of the speed of sound . . . . . . . . . . . . 473 (c) Object travels at 0.15 of the speed of sound . . . . . . . . . . . . 473 13.4 Flow through a converging diverging nozzle . . . . . . . . . . . . . . . 474 13.5 Perfect gas flows through a tube . . . . . . . . . . . . . . . . . . . . . 475 13.7 Control volume inside a converging-diverging nozzle . . . . . . . . . . . 476 13.6 Station properties as f (M ) . . . . . . . . . . . . . . . . . . . . . . . . 477 13.8 The relationship between the cross section and the Mach number . . . 481 13.9 Schematic to explain the significances of the Impulse function . . . . . 494 13.10Schematic of a flow through a nozzle example (13.11) . . . . . . . . . 495 13.11A shock wave inside a tube . . . . . . . . . . . . . . . . . . . . . . . . 496 13.12The Mexit and P0 as a function Mupstream . . . . . . . . . . . . . . . 502 13.13The ratios of the static properties of the two sides of the shock. . . . . 503 13.14Stationary and moving coordinates for the moving shock . . . . . . . . 505 (a) Stationary coordinates . . . . . . . . . . . . . . . . . . . . . . . 505 (b) Moving coordinates . . . . . . . . . . . . . . . . . . . . . . . . . 505 13.15The shock drag diagram for moving shock . . . . . . . . . . . . . . . . 507 13.16The diagram for the common explanation for shock drag . . . . . . . . 508 13.17Control volume for isothermal flow . . . . . . . . . . . . . . . . . . . . 512 13.18Working relationships for isothermal flow . . . . . . . . . . . . . . . . . 517 13.19Control volume of the gas flow in a constant cross section for Fanno Flow526 13.20Various parameters in fanno flow . . . . . . . . . . . . . . . . . . . . . 535 13.21Schematic of Example 13.18 . . . . . . . . . . . . . . . . . . . . . . . 536 13.22The schematic of Example (13.19) . . . . . . . . . . . . . . . . . . . . 538 fL 13.23The effects of increase of 4 D on the Fanno line . . . . . . . . . . . . 542 4f L 13.24The effects of the increase of D on the Fanno Line . . . . . . . . . . 543 13.25Min and m ˙ as a function of the 4fDL . . . . . . . . . . . . . . . . . . . 543 13.26M1 as a function M2 for various 4fDL . . . . . . . . . . . . . . . . . . . 545 13.27 M1 as a function M2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 fL 13.28 The pressure distribution as a function of 4 D . . . . . . . . . . . . 548 4f L 13.29Pressure as a function of long D . . . . . . . . . . . . . . . . . . . . 549 13.30 The effects of pressure variations on Mach number profile . . . . . . . 550 fL fL 13.31 Pressure ratios as a function of 4 D when the total 4 D = 0.3 . . . . 551 13.32 The extra tube length as a function of the shock location . . . . . . . 552 13.33 The maximum entrance Mach number as a function of 4fDL . . . . . 553 13.34 Unchoked flow showing the hypothetical “full” tube . . . . . . . . . . 557 fL 13.35Pressure ratio obtained for fix 4 D for k=1.4 . . . . . . . . . . . . . . 557 4f L 13.36Conversion of solution for given = 0.5 and pressure ratio . . . . . 559 D 13.37 The results of the algorithm showing the conversion rate . . . . . . . . 560 fL 13.38 M1 as a function of 4 D comparison with Isothermal Flow . . . . . . 562 13.39The control volume of Rayleigh Flow . . . . . . . . . . . . . . . . . . . 566 13.40The temperature entropy diagram for Rayleigh line . . . . . . . . . . . 568

xx

LIST OF FIGURES 13.41The basic functions of Rayleigh Flow (k=1.4) . . . . . . . . . . . . . . 574 13.42Schematic of the combustion chamber . . . . . . . . . . . . . . . . . . 579 14.1 A view of a normal shock as a limited case for oblique shock . 14.2 The oblique shock or Prandtl–Meyer function regions . . . . . 14.3 A typical oblique shock schematic . . . . . . . . . . . . . . . 14.4 Flow around spherically blunted 30◦ cone-cylinder . . . . . . . 14.5 The different views of a large inclination angle . . . . . . . . . 14.6 The three different Mach numbers . . . . . . . . . . . . . . . 14.7 The “imaginary” Mach waves at zero inclination . . . . . . . . 14.8 The possible range of solutions . . . . . . . . . . . . . . . . 14.9 Two dimensional wedge . . . . . . . . . . . . . . . . . . . . . 14.10 A local and a far view of the oblique shock. . . . . . . . . . 14.11 Oblique shock around a cone . . . . . . . . . . . . . . . . . 14.12 Maximum values of the properties in an oblique shock . . . . 14.13 Two variations of inlet suction for supersonic flow . . . . . . 14.14Schematic for Example (14.5) . . . . . . . . . . . . . . . . . . 14.15Schematic for Example (14.6) . . . . . . . . . . . . . . . . . . 14.16 Schematic of two angles turn with two weak shocks . . . . . 14.17Schematic for Example (14.11) . . . . . . . . . . . . . . . . . 14.18Illustration for Example (14.14) . . . . . . . . . . . . . . . . . 14.19 Revisiting of shock drag diagram for the oblique shock. . . . 14.21Definition of the angle for the Prandtl–Meyer function . . . . 14.22The angles of the Mach line triangle . . . . . . . . . . . . . . 14.20Oblique δ − θ − M relationship figure . . . . . . . . . . . . . 14.23The schematic of the turning flow . . . . . . . . . . . . . . . 14.24The mathematical coordinate description . . . . . . . . . . . . 14.25Prandtl-Meyer function after the maximum angle . . . . . . . 14.26The angle as a function of the Mach number . . . . . . . . . 14.27Diamond shape for supersonic d’Alembert’s Paradox . . . . . 14.28The definition of attack angle for the Prandtl–Meyer function 14.29Schematic for Example 14.5 . . . . . . . . . . . . . . . . . . . 14.30 Schematic for the reversed question of Example 14.17 . . . . 14.31 Schematic of the nozzle and Prandtl–Meyer expansion. . . .

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581 582 582 588 589 591 595 598 598 600 602 603 604 604 606 606 610 613 615 616 616 617 618 619 623 624 624 624 625 626 629

15.1 Different fields of multi phase flow . . . . . . . . . . . . . . . . . . 15.2 Stratified flow in horizontal tubes when the liquids flow is very slow 15.3 Kind of Stratified flow in horizontal tubes . . . . . . . . . . . . . . 15.4 Plug flow in horizontal tubes with the liquids flow is faster . . . . . 15.5 Modified Mandhane map for flow regime in horizontal tubes . . . . 15.6 Gas and liquid in Flow in verstical tube against the gravity . . . . . 15.7 A dimensional vertical flow map low gravity against gravity . . . . . 15.8 The terminal velocity that left the solid particles . . . . . . . . . . . 15.9 The flow patterns in solid-liquid flow . . . . . . . . . . . . . . . . . 15.11Counter–current flow in a can . . . . . . . . . . . . . . . . . . . . .

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633 635 636 636 637 638 639 649 650 651

LIST OF FIGURES

xxi

15.10Counter–flow in vertical tubes map . . . . . . . . . . . . . . . . . . . 15.12Image of counter-current flow in liquid–gas/solid–gas configurations. . 15.13Flood in vertical pipe . . . . . . . . . . . . . . . . . . . . . . . . . . 15.14A flow map to explain the horizontal counter–current flow . . . . . . 15.15A diagram to explain the flood in a two dimension geometry . . . . . 15.16General forces diagram to calculated the in a two dimension geometry

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651 652 652 653 654 659

A.1 A.2 A.3 A.4 A.5 A.6 A.7

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661 662 668 669 670 671 689

Vector in Cartesian coordinates system . . . . . . . . The right hand rule . . . . . . . . . . . . . . . . . . Cylindrical Coordinate System . . . . . . . . . . . . Spherical Coordinate System . . . . . . . . . . . . . The general Orthogonal with unit vectors . . . . . . Parabolic coordinates by user WillowW using Blender The tringle angles sides . . . . . . . . . . . . . . . .

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xxii

LIST OF FIGURES

Nomenclature ¯ R

Universal gas constant, see equation (2.26), page 50

τ

The shear stress Tenser, see equation (6.7), page 178

`

Units length., see equation (2.1), page 45

ˆ n

unit vector normal to surface of constant property, see equation (12.17), page 379

λ

bulk viscosity, see equation (8.101), page 263

M

Angular Momentum, see equation (6.39), page 199

µ

viscosity at input temperature, T, see equation (1.17), page 12

µ0

reference viscosity at reference temperature, Ti0 , see equation (1.17), page 12

F ext

External forces by non–fluids means, see equation (6.11), page 179

U

The velocity taken with the direction, see equation (6.1), page 177

ρ

Density of the fluid, see equation (13.1), page 437

Ξ

Martinelli parameter, see equation (15.43), page 615

A

The area of surface, see equation (4.140), page 111

a

The acceleration of object or system, see equation (4.0), page 69

Bf

Body force, see equation (2.9), page 47

BT

bulk modulus, see equation (13.16), page 440

c

Speed of sound, see equation (13.1), page 437

c.v.

subscribe for control volume, see equation (5.0), page 150

Cp

Specific pressure heat, see equation (2.23), page 49

Cv

Specific volume heat, see equation (2.22), page 49

E

Young’s modulus, see equation (13.17), page 440

EU

Internal energy, see equation (2.3), page 46

xxiii

xxiv

LIST OF FIGURES

Eu

Internal Energy per unit mass, see equation (2.6), page 47

Ei

System energy at state i, see equation (2.2), page 46

G

The gravitation constant, see equation (4.70), page 91

gG

general Body force, see equation (4.0), page 69

H

Enthalpy, see equation (2.18), page 48

h

Specific enthalpy, see equation (2.18), page 48

k

the ratio of the specific heats, see equation (2.24), page 49

kT

Fluid thermal conductivity, see equation (7.3), page 208

L

Angular momentum, see equation (3.41), page 65

M

Mach number, see equation (13.24), page 443

P

Pressure, see equation (13.3), page 437

Patmos Atmospheric Pressure, see equation (4.108), page 102 q

Energy per unit mass, see equation (2.6), page 47

Q12

The energy transferred to the system between state 1 and state 2, see equation (2.2), page 46

R

Specific gas constant, see equation (2.27), page 50

S

Entropy of the system, see equation (2.13), page 48

Suth

Suth is Sutherland’s constant and it is presented in the Table 1.1, see equation (1.17), page 12

Tτ

Torque, see equation (3.43), page 66

Ti0

reference temperature in degrees Kelvin, see equation (1.17), page 12

Tin

input temperature in degrees Kelvin, see equation (1.17), page 12

U

velocity , see equation (2.4), page 46

w

Work per unit mass, see equation (2.6), page 47

W12

The work done by the system between state 1 and state 2, see equation (2.2), page 46

z

the coordinate in z direction, see equation (4.15), page 72

says

Subscribe says, see equation (5.0), page 150

The Book Change Log Version 0.4 April 16, 2021 (11M 743 pages) • Add the new method for stability suggesting improve the older methods (a small revolution in floating body stability) (a new book on ship stability underway) • Add new change centroid location for added or subtracted masses (new concepts) • Several examples in mass conservation • minor correction for layout picture like better caption layout (improvements in potto.sty) • some additions not documented

Version 0.3.4.2 January 9, 2014 (8.8 M 682 pages) • The first that appear on the internet without pdf version. • Add two examples to Dimensional Analysis chapter.

Version 0.3.4.1 Dec 31, 2013 (8.9 M 666 pages) • The first Internet or php version. • Minor fixes and figures improvements.

Version 0.3.4.0 July 25, 2013 (8.9 M 666 pages) • Add the skeleton of inviscid flow xxv

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Version 0.3.3.0 March 17, 2013 (4.8 M 617 pages) • Add the skeleton of 2-D compressible flow • English and minor corrections in various chapters.

Version 0.3.2.0 March 11, 2013 (4.2 M 553 pages) • Add the skeleton of 1-D compressible flow • English and minor corrections in various chapters.

Version 0.3.1.1 Dec 21, 2011 (3.6 M 452 pages) • Minor additions to the Dimensional Analysis chapter. • English and minor corrections in various chapters.

Version 0.3.1.0 Dec 13, 2011 (3.6 M 446 pages) • Addition of the Dimensional Analysis chapter skeleton. • English and minor corrections in various chapters.

Version 0.3.0.4 Feb 23, 2011 (3.5 M 392 pages) • Insert discussion about Pushka equation and bulk modulus. • Addition of several examples integral Energy chapter. • English and addition of other minor examples in various chapters.

Version 0.3.0.3 Dec 5, 2010 (3.3 M 378 pages) • Add additional discussion about bulk modulus of geological system.

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• Addition of several examples with respect speed of sound with variation density under bulk modulus. This addition was to go the compressible book and will migrate to there when the book will brought up to code. • Brought the mass conservation chapter to code. • additional examples in mass conservation chapter.

Version 0.3.0.2 Nov 19, 2010 (3.3 M 362 pages) • Further improved the script for the chapter log file for latex (macro) process. • Add discussion change of bulk modulus of mixture. • Addition of several examples. • Improve English in several chapters.

Version 0.3.0.1 Nov 12, 2010 (3.3 M 358 pages) • Build the chapter log file for latex (macro) process Steven from www.artofproblemsolving.com. • Add discussion change of density on buck modulus calculations as example as integral equation. • Minimal discussion of converting integral equation to differential equations. • Add several examples on surface tension. • Improvement of properties chapter. • Improve English in several chapters.

Version 0.3.0.0 Oct 24, 2010 (3.3 M 354 pages) • Change the emphasis equations to new style in Static chapter. • Add discussion about inclined manometer • Improve many figures and equations in Static chapter. • Add example of falling liquid gravity as driving force in presence of shear stress. • Improve English in static and mostly in differential analysis chapter.

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Version 0.2.9.1 Oct 11, 2010 (3.3 M 344 pages) • Change the emphasis equations to new style in Thermo chapter. • Correct the ideal gas relationship typo thanks to Michal Zadrozny. • Add example, change to the new empheq format and improve cylinder figure. • Add to the appendix the differentiation of vector operations. • Minor correction to to the wording in page 11 viscosity density issue (thanks to Prashant Balan). • Add example to dif chap on concentric cylinders poiseuille flow.

Version 0.2.9 Sep 20, 2010 (3.3 M 338 pages) • Initial release of the differential equations chapter. • Improve the emphasis macro for the important equation and useful equation.

Version 0.2.6 March 10, 2010 (2.9 M 280 pages) • add example to Mechanical Chapter and some spelling corrected.

Version 0.2.4 March 01, 2010 (2.9 M 280 pages) • The energy conservation chapter was released. • Some additions to mass conservation chapter on averaged velocity. • Some additions to momentum conservation chapter. • Additions to the mathematical appendix on vector algebra. • Additions to the mathematical appendix on variables separation in second order ode equations. • Add the macro protect to insert figure in lower right corner thanks to Steven from www.artofproblemsolving.com.

• Add the macro to improve emphases equation thanks to Steven from www.artofproblemsolving

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• Add example about the the third component of the velocity. • English corrections, Thanks to Eliezer Bar-Meir

Version 0.2.3 Jan 01, 2010 (2.8 M 241 pages) • The momentum conservation chapter was released. • Corrections to Static Chapter. • Add the macro ekes to equations in examples thanks to Steven from www.artofproblemsolving.com. • English corrections, Thanks to Eliezer Bar-Meir

Version 0.1.9 Dec 01, 2009 (2.6 M 219 pages) • The mass conservation chapter was released. • Add Reynold’s Transform explanation. • Add example on angular rotation to statics chapter. • Add the open question concept. Two open questions were released. • English corrections, Thanks to Eliezer Bar-Meir

Version 0.1.8.5 Nov 01, 2009 (2.5 M 203 pages) • First true draft for the mass conservation. • Improve the dwarfing macro to allow flexibility with sub title. • Add the first draft of the temperature-velocity diagram to the Therm’s chapter.

Version 0.1.8.1 Sep 17, 2009 (2.5 M 197 pages) • Continue fixing the long titles issues. • Add some examples to static chapter. • Add an example to mechanics chapter.

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Version 0.1.8a July 5, 2009 (2.6 M 183 pages) • Fixing some long titles issues. • Correcting the gas properties tables (thanks to Heru and Micheal) • Move the gas tables to common area to all the books.

Version 0.1.8 Aug 6, 2008 (2.4 M 189 pages) • Add the chapter on introduction to muli–phase flow • Again additional improvement to the index (thanks to Irene). • Add the Rayleigh–Taylor instability. • Improve the doChap scrip to break up the book to chapters.

Version 0.1.6 Jun 30, 2008 (1.3 M 151 pages) • Fix the English in the introduction chapter, (thanks to Tousher). • Improve the Index (thanks to Irene). • Remove the multiphase chapter (it is not for public consumption yet).

Version 0.1.5a Jun 11, 2008 (1.4 M 155 pages) • Add the constant table list for the introduction chapter. • Fix minor issues (English) in the introduction chapter.

Version 0.1.5 Jun 5, 2008 (1.4 M 149 pages) • Add the introduction, viscosity and other properties of fluid. • Fix very minor issues (English) in the static chapter.

LIST OF FIGURES

Version 0.1.1 May 8, 2008 (1.1 M 111 pages) • Major English corrections for the three chapters. • Add the product of inertia to mechanics chapter. • Minor corrections for all three chapters.

Version 0.1a April 23, 2008 • The Thermodynamics chapter was released. • The mechanics chapter was released. • The static chapter was released (the most extensive and detailed chapter).

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Notice of Copyright This document is published under modified FDL. The change of the license is to prevent from situations that the author has to buy his own book. The Potto Project License doesn’t long apply to this document and associated documents.

GNU Free Documentation License The modification is that under section 3 “copying in quantity” should be add in the end. “If you intend to print and/or print more than 200 copies, you are required to furnish the author (with out cost to the author) with two (2) copies of the printed book within one month after the distributions or the printing is commenced.” If you convert the book to another electronic version you must provide a copy to the author of the new version within one month after the conversion. Version 1.2, November 2002 c Copyright 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Preamble The purpose of this License is to make a manual, textbook, or other functional and useful document ”free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. This License is a kind of ”copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software. We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with

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manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

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E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices. F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below. G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice. H. Include an unaltered copy of this License. I. Preserve the section Entitled ”History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled ”History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence. J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the ”History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission. K. For any section Entitled ”Acknowledgements” or ”Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein. L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles. M. Delete any section Entitled ”Endorsements”. Such a section may not be included in the Modified Version. N. Do not retitle any existing section to be Entitled ”Endorsements” or to conflict in title with any Invariant Section. O. Preserve any Warranty Disclaimers. If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.

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7. AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an ”aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document. If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

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9. TERMINATION You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/. Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License ”or any later

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version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: c Copyright YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no BackCover Texts. A copy of the license is included in the section entitled ”GNU Free Documentation License”.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the ”with...Texts.” line with this:

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If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

CONTRIBUTORS LIST How to contribute to this book As a copylefted work, this book is open to revisions and expansions by any interested parties. The only ”catch” is that credit must be given where credit is due. This is a copyrighted work: it is not in the public domain! If you wish to cite portions of this book in a work of your own, you must follow the same guidelines as for any other GDL copyrighted work.

Credits All entries have been arranged in alphabetical order of surname, hopefully. Major contributions are listed by individual name with some detail on the nature of the contribution(s), date, contact info, etc. Minor contributions (typo corrections, etc.) are listed by name only for reasons of brevity. Please understand that when I classify a contribution as ”minor,” it is in no way inferior to the effort or value of a ”major” contribution, just smaller in the sense of less text changed. Any and all contributions are gratefully accepted. I am indebted to all those who have given freely of their own knowledge, time, and resources to make this a better book! • Date(s) of contribution(s): 1999 to present • Nature of contribution: Original author. • Contact at: genick at potto.org

Steven from artofproblemsolving.com • Date(s) of contribution(s): June 2005, Dec, 2009 • Nature of contribution: LaTeX formatting, help on building the useful equation and important equation macros. • Nature of contribution: In 2009 creating the exEq macro to have different counter for example.

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Dan H. Olson • Date(s) of contribution(s): April 2008 • Nature of contribution: Some discussions about chapter on mechanics and correction of English.

Richard Hackbarth • Date(s) of contribution(s): April 2008 • Nature of contribution: Some discussions about chapter on mechanics and correction of English.

John Herbolenes • Date(s) of contribution(s): August 2009 • Nature of contribution: Provide some example for the static chapter.

Eliezer Bar-Meir • Date(s) of contribution(s): Nov 2009, Dec 2009 • Nature of contribution: Correct many English mistakes Mass. • Nature of contribution: Correct many English mistakes Momentum.

Henry Schoumertate • Date(s) of contribution(s): Nov 2009 • Nature of contribution: Discussion on the mathematics of Reynolds Transforms.

Your name here • Date(s) of contribution(s): Month and year of contribution • Nature of contribution: Insert text here, describing how you contributed to the book. • Contact at: my [email protected]

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Typo corrections and other ”minor” contributions • R. Gupta, January 2008, help with the original img macro and other ( LaTeX issues). • Tousher Yang April 2008, review of statics and thermo chapters. • Corretion to equation (2.38) by Michal Zadrozny. (Nov 2010) • Corretion to wording in viscosity density Prashant Balan. (Nov 2010)

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About This Author Genick Bar-Meir is a world–renowned and leading scientist who holds a Ph.D. in Mechanical Engineering from University of Minnesota and a Master in Fluid Mechanics from Tel Aviv University. Dr. Bar-Meir was the last student of the late Dr. R. G. E. Eckert (the same one who Ec number bear is name.). Bar-Meir is responsible for major advancements in Fluid mechanics (Pushka equation (deep ocean pressure), ship stability, etc.), particularly in the pedagogy of Fluid Mechanics curriculum. Currently, he writes books (there are already three very popular books), and provides freelance consulting of applications in various fields of fluid mechanics. According the Alexa(.com) and http://website-tools.net/ over 73% of the entire world download books are using Genick’s book. Bar-Meir also introduced a new methodology of Dimensional Analysis. Traditionally, Buckingham’s Pi theorem is used as an exclusive method of Dimensional Analysis. Bar-Meir demonstrated that the Buckingham method provides only the minimum number of dimensionless parameters. This minimum number of parameters is insufficient to understand almost any physical phenomenon. He showed that the improved Nusselt’s methods provides a complete number of dimensionless parameters and thus the key to understand the physical phenomenon. He extended Nusselt’s methods and made it the cornerstone in the new standard curriculum of Fluid Mechanics class. Recently, Bar-Meir developed a new foundation (theory) so that improved shock tubes can be built and utilized. This theory also contributes a new concept in thermodynamics, that of the pressure potential. Before that, one of the open question that remained in hydrostatics was what is the pressure at great depths. The previous common solution had been awkward and complex numerical methods. Bar-Meir provided an elegant analytical foundation (Pushka Equation) to compute the parameters in this phenomenon. This solution has practical applications in finding depth at great ocean depths and answering questions of geological scale problems. In the latest version a new, more accurate and hopefully a simpler method to calculate the stability was developed by Bar–Meir. Additionally, Bar–Meir has shown that the potential method has limitations because stability is compartmental which the way the potential energy structure. Bar-Meir provided a way to improves this limitation. In the area of compressible flow, it was commonly believed and taught that there is only weak and strong shock and it is continued by the Prandtl–Meyer function. Bar–Meir discovered the analytical solution for oblique shock and showed that there is a “quiet” zone between the oblique shock and Prandtl–Meyer (isentropic expansion) flow. He also built analytical solution to several moving shock cases. He described

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and categorized the filling and evacuating of chamber by compressible fluid in which he also found analytical solutions to cases where the working fluid was an ideal gas. The common explanation to Prandtl–Meyer function shows that flow can turn in a sharp corner. Engineers have constructed a design that is based on this conclusion. Bar-Meir demonstrated that common Prandtl–Meyer explanation violates the conservation of mass and therefore the turn must be a round and finite radius. The author’s explanations on missing diameter and other issues in Fanno flow and “naughty professor’s question” are commonly used in various industries. Earlier, Bar-Meir made many contributions to the manufacturing process and economy and particularly in the die casting area. This work is used as a base in many numerical works, in USA (for example, GM), British industries, Spain, and Canada. Bar-Meir’s contributions to the understanding of the die casting process made him the main leading figure in that area. Initially in his career, Bar–Meir developed a new understanding of Mass Transfer in high concentrations which are now standard building blocks for more complex situations. For some time Bar-Meir has worked on project like rain barrels design, extraction energy form breaking system, die casting design improvement for some private companies. While the extraction energy project provide interesting problems it will not be produce as much academic advancement because commercial secrecy. In fact, if you interested in developing these patents you can contact this author (for example extraction of energy from breaking system has estimated value of hundred of Billions). These hand–on projects where a great enjoyment and exposed various issues that otherwise were not on the radar of this author. These “strange” projects leads to new understanding in ship stability (floating bodies). For example, the stability of floating cylinder is for the first time was solved analytically. The author used to live with his wife and three children. Now his kids are in medical school or already pass that stage and are on medical career. This fact is a demonstration that while you can get your kids to understand calculus and do AP in elementary school, you still can fall their education. A past project of his was building a four stories house, practically from scratch. While he writes his programs and does other computer chores, he often feels clueless about computers and programming. While he is known to look like he knows about many things, the author just know to learn quickly. The author spent years working on the sea (ships) as a engine sea officer but now the author prefers to remain on solid ground.

Prologue For This Book Version 0.4 April 6, 2020 pages 749 size 11M What a change and what a strange experience was to write this book. I got many publishers who told me that I need to “hand over” them the book copyright and in return they will allow me to use 50% even more of the book. The most bizarre “offer” was from University of Washington Seattle from mechanical engineering department. They told me that I must hand over the copyright and that I should be happy if they take over writing the book because they more qualify than me because they have a member in the national academy. Perhaps the strange of all was what occur in the following. The theory I developed on great depth pressure (Pushka’s equation) was taught to my relative for two or three lectures in a famous north Chicagoland private University. The instructor from mechanical engineering taught this material (Pushka’s Equation) and was using almost verbatim copy of the example including my nomenclature (from this book) without acknowledgment. While is flattering that the instructor was plagiarizing my material, it is disturbing that he and others like him violating the copyright of open content material.

Version 0.3.2.0 March 18, 2013 pages 617 size 4.8M It is nice to see that the progress of the book is about 100 pages per year. As usual, the book contains new material that was not published before. While in the near future the focus will be on conversion to php, the main trust is planed to be on add several missing chapters. potto.sty was improved and subUsefulEquaiton was defined. For the content point of view two main chapters were add.

Version 0.3.0.5 March 1, 2011 pages 400 size 3.5M A look on the progress which occur in the two and half years since the last time this page has been changed, shows that the book scientific part almost tripled. Three new chapters were added included that dealing with integral analysis and one chapter

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on differential analysis. Pushka equation (equation describing the density variation in great depth for slightly compressible material) was added yet not included in any other textbook. While the chapter on the fluid static is the best in the world (according to many including this author1 ), some material has to be expanded. The potto style file has improved and including figures inside examples. Beside the Pushka equation, the book contains material that was not published in other books. Recently, many heavy duty examples were enhanced and thus the book quality. The meaning heavy duty example refers here to generalized cases. For example, showing the instability of the upside cone versus dealing with upside cone with specific angle.

Version 0.1.8 August 6, 2008 pages 189 size 2.6M When this author was an undergraduate student, he spend time to study the wave phenomenon at the interface of open channel flow. This issue is related to renewal energy of extracting energy from brine solution (think about the Dead Sea, so much energy). The common explanation to the wave existence was that there is always a disturbance which causes instability. This author was bothered by this explanation. Now, in this version, it was proven that this wavy interface is created due to the need to satisfy the continuous velocity and shear stress at the interface and not a disturbance. Potto project books are characterized by high quality which marked by presentation of the new developments and clear explanations. This explanation (on the wavy interface) demonstrates this characteristic of Potto project books. The introduction to multi–phase is another example to this quality. While it is a hard work to discover and develop and bring this information to the students, it is very satisfying for the author. The number of downloads of this book results from this quality. Even in this early development stage, number of downloads per month is about 5000 copies.

Version 0.1 April 22, 2008 pages 151 size 1.3M The topic of fluid mechanics is common to several disciplines: mechanical engineering, aerospace engineering, chemical engineering, and civil engineering. In fact, it is also related to disciplines like industrial engineering, and electrical engineering. While the emphasis is somewhat different in this book, the common material is presented and hopefully can be used by all. One can only admire the wonderful advances done by the previous geniuses who work in this field. In this book it is hoped to insert, what and when a certain model is suitable than other models. One of the difference in this book is the insertion of the introduction to multiphase flow. Clearly, multiphase is an advance topic. However, some minimal 1 While this bragging is not appropriate in this kind of book it is to point the missing and additional further improvements needed.

VERSION 0.1 APRIL 22, 2008

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familiarity can be helpful for many engineers who have to deal with non pure single phase fluid. This book is the third book in the series of POTTO project books. POTTO project books are open content textbooks so everyone are welcome to joint in. The topic of fluid mechanics was chosen just to fill the introduction chapter to compressible flow. During the writing it became apparent that it should be a book in its own right. In writing the chapter on fluid statics, there was a realization that it is the best chapter written on this topic. It is hoped that the other chapters will be as good this one. This book is written in the spirit of my adviser and mentor E.R.G. Eckert. Eckert, aside from his research activity, wrote the book that brought a revolution in the education of the heat transfer. Up to Egret’s book, the study of heat transfer was without any dimensional analysis. He wrote his book because he realized that the dimensional analysis utilized by him and his adviser (for the post doc), Ernst Schmidt, and their colleagues, must be taught in engineering classes. His book met strong criticism in which some called to “burn” his book. Today, however, there is no known place in world that does not teach according to Eckert’s doctrine. It is assumed that the same kind of individual(s) who criticized Eckert’s work will criticize this work. Indeed, the previous book, on compressible flow, met its opposition. For example, anonymous Wikipedia user name EMBaero claimed that the material in the book is plagiarizing, he just doesn’t know from where and what. Maybe that was the reason that he felt that is okay to plagiarize the book on Wikipedia. These criticisms will not change the future or the success of the ideas in this work. As a wise person says “don’t tell me that it is wrong, show me what is wrong”; this is the only reply. With all the above, it must be emphasized that this book is not expected to revolutionize the field but change some of the way things are taught. The book is organized into several chapters which, as a traditional textbook, deals with a basic introduction to the fluid properties and concepts (under construction). The second chapter deals with Thermodynamics. The third book chapter is a review of mechanics. The next topic is statics. When the Static Chapter was written, this author did not realize that so many new ideas will be inserted into this topic. As traditional texts in this field, ideal flow will be presented with the issues of added mass and added forces (under construction). The classic issue of turbulence (and stability) will be presented. An introduction to multi–phase flow, not a traditional topic, will be presented next (again under construction). The next two chapters will deals with open channel flow and gas dynamics. At this stage, dimensional analysis will be present (again under construction).

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LIST OF FIGURES

How This Book Was Written 2021 Version Many of the programs that were used initially in the book matured like vim currently version 8 and up. Some other programs like tgif were replaced by other like ipe and blender. The main change is that the material comes more from the industry. There are more examples that originated from problems that were encounter in the industry. Well probably the engagement with one work reflects in its writing. It is a hope that this material will be well received as before.

Initial This book started because I needed an introduction to the compressible flow book. After a while it seems that is easier to write a whole book than the two original planned chapters. In writing this book, it was assumed that introductory book on fluid mechanics should not contained many new ideas but should be modern in the material presentation. There are numerous books on fluid mechanics but none is open content. The approach adapted in this book is practical, and more hands–on approach. This statement really meant that the book is intent to be used by students to solve their exams and also used by practitioners when they search for solutions for practical problems. So, issue of proofs so and so are here only either to explain a point or have a solution of exams. Otherwise, this book avoids this kind of issues. The structure of Hansen, Streeter and Wylie, and Shames books were adapted and used as a scaffolding for this book. This author was influenced by Streeter and Wylie book which was his undergrad textbooks. The chapters are not written in order. The first 4 chapters were written first because they were supposed to be modified and used as fluid mechanics introduction in “Fundamentals of Compressible Flow.” Later, multi–phase flow chapter was written. The chapter on ideal flow was add in the later stage. The presentation of some of the chapters is slightly different from other books because the usability of the computers. The book does not provide the old style graphical solution methods yet provides the graphical explanation of things. Of course, this book was written on Linux (Micro$oftLess book). This book was written using the vim editor for editing (sorry never was able to be comfortable with emacs). The graphics were done by TGIF, the best graphic program that this author experienced so far. The figures were done by GLE. The spell checking was done by

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LIST OF FIGURES

ispell, and hope to find a way to use gaspell, a program that currently cannot be used on new Linux systems. The figure in cover page was created by Genick Bar-Meir, and is copyleft by him. Over the time the book introduced me to others and make me engaged in topics that I was not aware off. For example, the issue rain barrels design leads to several examples dimensional analyses in the book. Another example, work on how to convert the breaking energy of cars (consider the change of millage per gallon between the city and the highway). This brought to the realization the maximum temperature theory. Unfortunately the work finished before it complete due to lack of funding.

Preface "In the beginning, the POTTO project was and void; and emptiness was upon the face and files. And the Fingers of the Author the face of the keyboard. And the Author there be words, and there were words." 2 .

without form, of the bits moved upon said, Let

This book, Basics of Fluid Mechanics, describes the fundamentals of fluid mechanics phenomena for engineers and others. This book is designed to replace all introductory textbook(s) or instructor’s notes for the fluid mechanics in undergraduate classes for engineering/science students but also for technical peoples. It is hoped that the book could be used as a reference book for people who have at least some basics knowledge of science areas such as calculus, physics, etc. The structure of this book is such that many of the chapters could be usable independently. For example, if you need information about, say, statics’ equations, you can read just chapter (4). I hope this approach makes the book easier to use as a reference manual. However, this manuscript is first and foremost a textbook, and secondly a reference manual only as a lucky coincidence. I have tried to describe why the theories are the way they are, rather than just listing “seven easy steps” for each task. This means that a lot of information is presented which is not necessary for everyone. These explanations have been marked as such and can be skipped.3 Reading everything will, naturally, increase your understanding of the many aspects of fluid mechanics. Many in the industry, have called and emailed this author with questions since this book is only source in the world of some information. These questions have lead to more information and further explanation that is not found anywhere else. This book is written and maintained on a volunteer basis. Like all volunteer work, there is a limit on how much effort I was able to put into the book and its organization. Moreover, due to the fact that English is my third language and time limitations, the explanations are not as good as if I had a few years to perfect them. Nevertheless, I believe professionals working in many engineering fields will benefit from this information. This book contains many worked examples, which can be very useful for many. In fact, this book contains material that was not published anywhere else. As demonstration, some of the work was plagiarized in famous American universities. I have left some issues which have unsatisfactory explanations in the book, marked with a Mata mark. I hope to improve or to add to these areas in the near future. 2 To

the power and glory of the mighty God. This book is only attempt to explain his power. the present, the book is not well organized. You have to remember that this book is a work in progress. 3 At

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LIST OF FIGURES

Furthermore, I hope that many others will participate of this project and will contribute to this book (even small contributions such as providing examples or editing mistakes are needed). I have tried to make this text of the highest quality possible and am interested in your comments and ideas on how to make it better. Incorrect language, errors, ideas for new areas to cover, rewritten sections, more fundamental material, more mathematics (or less mathematics); I am interested in it all. I am particularly interested in the best arrangement of the book. If you want to be involved in the editing, graphic design, or proofreading, please drop me a line. You may contact me via Email at “[email protected]”. Naturally, this book contains material that never was published before (sorry cannot avoid it). This material never went through a close content review. While close content peer review and publication in a professional publication is excellent idea in theory. In practice, this process leaves a large room to blockage of novel ideas and plagiarism. If you would like be “peer reviews” or critic to my new ideas please send me your comment(s). Even reaction/comments from individuals like David Marshall4 . Several people have helped me with this book, directly or indirectly. I would like to especially thank to my adviser, Dr. E. R. G. Eckert, whose work was the inspiration for this book. I also would like to thank to Jannie McRotien (Open Channel Flow chapter) and Tousher Yang for their advices, ideas, and assistance. The symbol META was added to provide typographical conventions to blurb as needed. This is mostly for the author’s purposes and also for your amusement. There are also notes in the margin, but those are solely for the author’s purposes, ignore them please. They will be removed gradually as the version number advances. I encourage anyone with a penchant for writing, editing, graphic ability, LATEX knowledge, and material knowledge and a desire to provide open content textbooks and to improve them to join me in this project. If you have Internet e-mail access, you can contact me at “[email protected]”.

4 Dr. Marshall wrote to this author that the author should review other people work before he write any thing new (well, literature review is always good, isn’t it?). Over ten individuals wrote me about this letter. I am asking from everyone to assume that his reaction was innocent one. While his comment looks like unpleasant reaction, it brought or cause the expansion of the explanation for the oblique shock. However, other email that imply that someone will take care of this author aren’t appreciated.

To Do List and Road Map This book isn’t complete and probably never will be completed. There will always new problems to add or to polish the explanations or include more new materials. Also issues that associated with the book like the software has to be improved. It is hoped the changes in TEX and LATEX related to this book in future will be minimal and minor. It is hoped that the style file will be converged to the final form rapidly. Nevertheless, there are specific issues which are on the “table” and they are described herein. At this stage, some chapters are missing. Specific missing parts from every chapters are discussed below. These omissions, mistakes, approach problems are sometime appears in the book when possible. You are always welcome to add a new material: problem, question, illustration or photo of experiment. Material can be further illuminate. Additional material can be provided to give a different angle on the issue at hand.

Properties The chapter in beta stage and will be boosted in the future.

Turbulence To add this chapter.

Inviscid Flow To add the unsteady Bernoulli in moving frames To add K–J condition and Add properties.

Machinery To add this chapter.

Internal Viscous Flow To add this Chapter.

VERSION 0.1 APRIL 22, 2008

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Open Channel Flow The chapter isn’t in the development stage yet. Some parts were taken from Fundamentals of Die Casting Design book and are in a process of improvement.

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LIST OF FIGURES

1

Introduction to Fluid Mechanics 1.1 What is Fluid Mechanics?

Fluid mechanics deals with the study of all fluids under static and dynamic situations. Fluid mechanics is a branch of continuous mechanics which deals with a relationship between forces, motions, and statical conditions in a continuous material. This study area deals with many and diversified problems such as surface tension, fluid statics, flow in enclose bodies, or flow round bodies (solid or otherwise), flow stability, etc. In fact, almost any action a person is doing involves some kind of a fluid mechanics problem. Furthermore, the boundary between the solid mechanics and fluid mechanics is some kind of gray shed and not a sharp distinction (see Figure 1.1 for the complex relationships between the different branches which only part of it should be drawn in the same time.). For example, glass appears as a solid material, but a closer look reveals that the glass is a liquid with a large viscosity. A proof of the glass “liquidity” is the change of the glass thickness in high windows in European Churches after hundred years. The bottom part of the glass is thicker than the top part. Materials like sand (some call it quick sand) and grains should be treated as liquids. It is known that these materials have the ability to drown people. Even material such as aluminum just below the mushy zone1 also behaves as a liquid similarly to butter. Furthermore, material particles that “behaves” as solid mixed with liquid creates a mixture that behaves as a complex2 liquid. After it was established that the boundaries of fluid mechanics aren’t sharp, most of the discussion in this book is limited to simple and (mostly) Newtonian (sometimes power fluids) fluids which will be defined later. 1 Mushy 2 It

zone refers to aluminum alloy with partially solid and partially liquid phases. can be viewed as liquid solid multiphase flow.

1

2

CHAPTER 1. INTRODUCTION TO FLUID MECHANICS

Continuous Mechanics

Solid Mechanics

something between

Fluid Mechanics

ρ 6= constant

Fluid Statics

Fluid Dynamics

Boundaries problems Multi phase flow

Stability problems

Internal Flow Laminar Flow

Turbulent Flow

Fig. -1.1. Diagram to explain part of relationships of fluid mechanics branches.

1.2. BRIEF HISTORY

3

The fluid mechanics study involve many fields that have no clear boundaries between them. Researchers distinguish between orderly flow and chaotic flow as the laminar flow and the turbulent flow. The fluid mechanics can also be distinguish between a single phase flow and multiphase flow (flow made more than one phase or single distinguishable material). The last boundary (as all the boundaries in fluid mechanics) isn’t sharp because fluid can go through a phase change (condensation or evaporation) in the middle or during the flow and switch from a single phase flow to a multi phase flow. Moreover, flow with two phases (or materials) can be treated as a single phase (for example, air with dust particle). After it was made clear that the boundaries of fluid mechanics aren’t sharp, the study must make arbitrary boundaries between fields. Then the dimensional analysis can be used explain why in certain cases one distinguish area/principle is more relevant than the other and some effects can be neglected. Or, when a general model is need because more parameters are effecting the situation. It is this author’s personal experience that the knowledge and ability to know in what area the situation lay is one of the main problems. For example, engineers in software company (EKK Inc, http://ekkinc. com/ ) analyzed a flow of a complete still liquid assuming a complex turbulent flow model. Such absurd analysis are common among engineers who do not know which model can be applied. Thus, one of the main goals of this book is to explain what model should be applied. Before dealing with the boundaries, the simplified private cases must be explained. There are two main approaches of presenting an introduction of fluid mechanics materials. The first approach introduces the fluid kinematic and then the basic governing equations, to be followed by stability, turbulence, boundary layer and internal and external flow. The second approach deals with the Integral Analysis to be followed with Differential Analysis, and continue with Empirical Analysis. These two approaches pose a dilemma to anyone who writes an introductory book for the fluid mechanics. These two approaches have justifications and positive points. Reviewing many books on fluid mechanics made it clear, there isn’t a clear winner. This book attempts to find a hybrid approach in which the kinematic is presented first (aside to standard initial four chapters) follow by Integral analysis and continued by Differential analysis. The ideal flow (frictionless flow) should be expanded compared to the regular treatment. This book is unique in providing chapter on multiphase flow. Naturally, chapters on open channel flow (as a sub class of the multiphase flow) and compressible flow (with the latest developments) are provided.

1.2 Brief History The need to have some understanding of fluid mechanics started with the need to obtain water supply. For example, people realized that wells have to be dug and crude pumping devices need to be constructed. Later, a large population created a need to solve waste (sewage) and some basic understanding was created. At some point, people realized that water can be used to move things and provide power. When cities increased to a larger size, aqueducts were constructed. These aqueducts reached their greatest size

4

CHAPTER 1. INTRODUCTION TO FLUID MECHANICS

and grandeur in those of the City of Rome and China. Yet, almost all knowledge of the ancients can be summarized as application of instincts, with the exception Archimedes (250 B.C.) on the principles of buoyancy. For example, larger tunnels built for a larger water supply, etc. There were no calculations even with the great need for water supply and transportation. The first progress in fluid mechanics was made by Leonardo Da Vinci (1452-1519) who built the first chambered canal lock near Milan. He also made several attempts to study the flight (birds) and developed some concepts on the origin of the forces. After his initial work, the knowledge of fluid mechanics (hydraulic) increasingly gained speed by the contributions of Galileo, Torricelli, Euler, Newton, Bernoulli family, and D’Alembert. At that stage theory and experiments had some discrepancy. This fact was acknowledged by D’Alembert who stated that, “The theory of fluids must necessarily be based upon experiment.” For example the concept of ideal liquid that leads to motion with no resistance, conflicts with the reality. This discrepancy between theory and practice is called the “D’Alembert paradox” and serves to demonstrate the limitationsof theory alone in solving fluid problems. As in thermodynamics, two different of school of thoughts were created: the first believed that the solution will come from theoretical aspect alone, and the second believed that solution is the pure practical (experimental) aspect of fluid mechanics. On the theoretical side, considerable contribution were made by Euler, La Grange, Helmholtz, Kirchhoff, Rayleigh, Rankine, and Kelvin. On the “experimental” side, mainly in pipes and open channels area, were Brahms, Bossut, Chezy, Dubuat, Fabre, Coulomb, Dupuit, d’Aubisson, Hagen, and Poisseuille. In the middle of the nineteen century, first Navier in the molecular level and later Stokes from continuous point of view succeeded in creating governing equations for real fluid motion. Thus, creating a matching between the two school of thoughts: experimental and theoretical. But, as in thermodynamics, people cannot relinquish control. As results it created today “strange” names: Hydrodynamics, Hydraulics, Gas Dynamics, and Aeronautics. The Navier-Stokes equations, which describes the flow (or even Euler equations), were considered unsolvable during the mid nineteen century because of the high complexity. This problem led to two consequences. Theoreticians tried to simplify the equations and arrive at approximated solutions representing specific cases. Examples of such work are Hermann von Helmholtz’s concept of vortexes (1858), Lanchester’s concept of circulatory flow (1894), and the Kutta–Joukowski circulation theory of lift (1906). The experimentalists, at the same time proposed many correlations to many fluid mechanics problems, for example, resistance by Darcy, Weisbach, Fanning, Ganguillet, and Manning. The obvious happened without theoretical guidance, the empirical formulas generated by fitting curves to experimental data (even sometime merely presenting the results in tabular form) resulting in formulas that the relationship between the physics and properties made very little sense. At the end of the twenty century, the demand for vigorous scientific knowledge that can be applied to various liquids as opposed to formula for every fluid was created by the expansion of many industries. This demand coupled with new several novel

1.3. KINDS OF FLUIDS

5

concepts like the theoretical and experimental researches of Reynolds, the development of dimensional analysis by Rayleigh, and Froude’s idea of the use of models change the science of the fluid mechanics. Perhaps the most radical concept that effects the fluid mechanics is of Prandtl’s idea of boundary layer which is a combination of the modeling and dimensional analysis that leads to modern fluid mechanics. Therefore, many call Prandtl as the father of modern fluid mechanics. This concept leads to mathematical basis for many approximations. Thus, Prandtl and his students Blasius, von Karman, Meyer, and Blasius and several other individuals as Nikuradse, Rose, Taylor, Bhuckingham, Stanton, and many others, transformed the fluid mechanics to today modern science. While the understanding of the fundamentals did not change much, after World War Two, the way how it was calculated changed. The introduction of the computers during the 60s and much more powerful personal computer has changed the field. There are many open source programs that can analyze many fluid mechanics situations. Today many problems can be analyzed by using the numerical tools and provide reasonable results. These programs in many cases can capture all the appropriate parameters and adequately provide a reasonable description of the physics. However, there are many other cases that numerical analysis cannot provide any meaningful result (trends). For example, no weather prediction program can produce good engineering quality results (where the snow will fall within 50 kilometers accuracy. Building a car with this accuracy is a disaster). In the best scenario, these programs are as good as the input provided. Thus, assuming turbulent flow for still flow simply provides erroneous results (see for example, EKK, Inc).

1.3 Kinds of Fluids Some differentiate fluid from solid by the reaction to shear stress. The fluid continuously and permanently deformed under shear stress while the solid exhibits a finite deformation which does not change with time. It is also said that fluid cannot return to their original state after the deformation. This differentiation leads to three groups of materials: solids and liquids and all material between them. This test creates a new material group that shows dual behaviors; under certain limits; it behaves like solid and under others it behaves like fluid (see Fig. 1.1). The study of this kind of material called rheology and it will (almost) not be discussed in this book. It is evident from this discussion that when a fluid is at rest, no shear stress is applied. The fluid is mainly divided into two categories: liquids and gases.The main difference between the liquids and gases state is that gas will occupy the whole volume while liquids has an almost fix volume. This difference can be, for most practical purposes considered, sharp even though in reality this difference isn’t sharp. The difference between a gas phase to a liquid phase above the critical point are practically minor. But below the critical point, the change of water pressure by 1000% only change the volume by less than 1 percent. For example, a change in the volume by more 5% will required tens of thousands percent change of the pressure. So, if the change of pressure is significantly less than that, then the change of volume is at best 5%. Hence, the pressure

6

CHAPTER 1. INTRODUCTION TO FLUID MECHANICS

will not affect the volume. In gaseous phase, any change in pressure directly affects the volume. The gas fills the volume and liquid cannot. Gas has no free interface/surface (since it does fill the entire volume). There are several quantities that have to be addressed in this discussion. The first is force which was reviewed in physics. The unit used to measure is [N ]. It must be remember that force is a vector, e.g it has a direction. The second quantity discussed here is the area.This quantity was discussed in physics class but here it has an additional meaning, and it is referred to the direction of the area. The direction of area is perpendicular to the area. The area is measured in [m2 ]. Area of three–dimensional object has no single direction. Thus, these kinds of areas should be addressed infinitesimally and locally. The traditional quantity, which is force per area has a new meaning. This is a result of division of a vector by a vector and it is referred to as tensor. In this book, the emphasis is on the physics, so at this stage the tensor will have to be broken into its components. Later, the discussion on the mathematical meaning is presented (later version). For the discussion here, the pressure has three components, one in the area direction and two perpendicular to the area. The pressure component in the area direction is called pressure (great way to confuse, isn’t it?). The other two components are referred as the shear stresses. The units used for the pressure components is [N/m2 ]. The density is a property which requires that ρ liquid to be continuous. The density can be changed and it is a function of time and space (location) but must have a continues property. It doesn’t mean that ǫ a sharp and abrupt change in the density cannot occur. It referred to the fact that density is independent of the sampling size. Figure 1.2 shows the density as log ℓ a function of the sample size. After certain sample size, the density remains constant. Thus, the density is defined as Fig. -1.2. Density as a function of ρ=

∆m ∆V −→ε ∆V lim

the size of sample.

(1.1)

It must be noted that ε is chosen so that the continuous assumption is not broken, that is, it did not reach/reduced to the size where the atoms or molecular statistical calculations are significant (see Figure 1.2 for point where the green lines converge to constant density). When this assumption is broken, then, the principles of statistical mechanics must be utilized.

1.4 Shear Stress

1.4. SHEAR STRESS

7

The shear stress is part of the pressure tensor. ∆ℓ U0x F However, here, and many parts of the book, it will be treated as a separate issue. In solid mechanics, the shear stress is considered as the rah β tio of the force acting on area in the direction of y x the forces perpendicular to area (Note what the direction of area?). Different from solid, fluid Fig. -1.3. Schematics to describe cannot pull directly but through a solid surface. the shear stress in fluid mechanics. Consider liquid that undergoes a shear stress between a short distance of two plates as shown in Fig. 1.3. The upper plate velocity generally will be U = f (A, F, h)

(1.2)

Where A is the area, the F denotes the force, h is the distance between the plates. In this discussion, the aim is to develop differential equation, thus the small distance analysis is applicable. From solid mechanics study, it was shown that when the force per area increases, the velocity of the plate increases also. Experiments show that the increase of height will increase the velocity up to a certain range. Moving the plate with a zero lubricant (h ∼ 0) results in a large force or conversely a large amount of lubricant results in smaller force. For cases where the dependency is linear, the following can be written hF A

(1.3)

U F ∝ h A

(1.4)

F A

(1.5)

U∝ Equations (1.3) can be rearranged to be

Shear stress was defined as τxy =

The index x represent the “direction of the shear stress while the y represent the direction of the area(perpendicular to the area). From equations (1.4) and (1.5) it follows that ratio of the velocity to height is proportional to shear stress. Hence, applying the coefficient to obtain a new equality as τxy = µ

U h

(1.6)

Where µ is called the absolute viscosity or dynamic viscosity which will be discussed later in this chapter in a great length.

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CHAPTER 1. INTRODUCTION TO FLUID MECHANICS

In steady state, the distance the upper plate moves after small amount of time, δt is d` = U δt

geometry

d` = U δt =

t1 < t2

End Solution

Example 13.5: Gas flows through a converging–diverging duct. At point “A” the cross section area is 50 [cm2 ] and the Mach number was measured to be 0.4. At point B in the duct the cross section area is 40 [cm2 ]. Find the Mach number at point B. Assume that the flow is isentropic and the gas specific heat ratio is 1.4. Solution To obtain the Mach number at point B by finding the ratio of the area to the critical area. This relationship can be obtained by AB AB AA 40 = × ? = × A∗ AA A 50

from the Table 13.2

z }| { 1.59014

= 1.272112

5 Well, this question is for academic purposes, there is no known way for the author to directly measure the Mach number. The best approximation is by using inserted cone for supersonic flow and measure the oblique shock. Here it is subsonic and this technique is not suitable. 6 This pressure is about two atmospheres with temperature of 250[K]

484

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

B With the value of A A? from the Table 13.2 or from Potto-GDC two solutions can be obtained. The two possible solutions: the first supersonic M = 1.6265306 and second subsonic M = 0.53884934. Both solution are possible and acceptable. The supersonic branch solution is possible only if there where a transition at throat where M=1.

M 1.6266

ρ ρ0

T T0

A A?

0.65396 0.34585 1.2721

0.53887 0.94511 0.86838 1.2721

P P0

A×P A∗ ×P0

0.22617 0.28772 0.82071 1.0440

End Solution

Example 13.6: Engineer needs to redesign a syringe for medical applications. They complained that the syringe is “hard to push.” The engineer analyzes the flow and conclude that the flow is choke. Upon this fact, what engineer should do with the syringe; increase the pushing diameter or decrease the diameter? Explain. Solution This problem is a typical to compressible flow in the sense the solution is opposite the regular intuition. The diameter should be decreased. The pressure in the choke flow in the syringe is past the critical pressure ratio. Hence, the force is a function of the cross area of the syringe. So, to decrease the force one should decrease the area. End Solution

13.4.5

Mass Flow Rate (Number)

One of the important engineering parameters is the mass flow rate which for ideal gas is m ˙ = ρU A =

P UA RT

(13.50)

This parameter is studied here, to examine the maximum flow rate and to see what is the effect of the compressibility on the flow rate. The area ratio as a function of the Mach number needed to be established, specifically and explicitly the relationship for the chocked flow. The area ratio is defined as the ratio of the cross section at any point to the throat area (the narrow area). It is convenient to rearrange the equation (13.50) to be expressed in terms of the stagnation properties as f (M, k)

P P0 U m ˙ √ = A P0 k R T

r

k R

r

T0 1 P √ = √0 M T T0 T0

r

z r }| { k P T0 R P0 T

(13.51)

13.4. ISENTROPIC FLOW

485

Expressing the temperature in terms of Mach number in equation (13.51) results in m ˙ = A



k M P0 √ k R T0

 − k+1 2 (k−1) k−1 2 1+ M 2

(13.52)

It can be noted that equation (13.52) holds everywhere in the converging-diverging duct and this statement also true for the throat. The throat area can be denoted as by A∗ . It can be noticed that at the throat when the flow is chocked or in other words M = 1 and that the stagnation conditions (i.e. temperature, pressure) do not change. Hence equation (13.52) obtained the form ! √ − k+1 2 (k−1) kP0 m ˙ k−1 = √ (13.53) 1+ ∗ A 2 RT0 Since the mass flow rate is constant in the duct, dividing equations (13.53) by equation (13.52) yields Mass Flow Rate Ratio !− k+1 2 (k−1) 2 M 1 1 + k−1 A 2 = (13.54) k+1 A∗ M 2 Equation (13.54) relates the Mach number at any point to the cross section area ratio. The maximum flow rate can be expressed either by taking the derivative of equation (13.53) in with respect to M and equating to zero. Carrying this calculation results at M = 1. r  k+1   − 2(k−1) m ˙ P0 k k+1 √ = (13.55) A∗ max T0 R 2 For specific heat ratio, k = 1.4 

m ˙ A∗



max

0.68473 P √0 ∼ √ T0 R

The maximum flow rate for air (R = 287

(13.56)

j ) becomes, kg K

√ m ˙ T0 = 0.040418 A ? P0

(13.57)

Equation (13.57) is known as Fliegner’s Formula on the name of one of the first engineers who observed experimentally the choking phenomenon. It can be noticed that Fliegner’s equation can lead to definition of the Fliegner’s Number. c

Fn zp }|0 { z }| { m ˙ T0 m ˙ k R T0 1 m ˙ c0 1 √ = √ =√ A ∗ P0 R A ∗ P0 k k RA∗ P0

√

(13.58)

486

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

The definition of Fliegner’s number (Fn) is √ Rm ˙ c0 Fn ≡ √ R A ∗ P0

(13.59)

Utilizing Fliegner’s number definition and substituting it into equation (13.53) results in Fliegner’s Number k+1  − 2(k−1) k−1 2 Fn = k M 1 + (13.60) M 2 and the maximum point for F n at M = 1 is k+1  − 2(k−1) k+1 Fn = k 2

(13.61)

Example 13.7: Why F n is zero at Mach equal to zero? Prove Fliegner number, F n is maximum at M = 1. Thus, R T0 P2



m ˙ A

2

=

F n2 k



A ∗ P0 AP

2

(13.62)

Example 13.8: The pitot tube measured the temperature of a flow which was found to be 300◦ C. The static pressure was measured to be 2 [Bar]. The flow rate is 1 [kg/sec] and area of the conduct is 0.001 [m2 ]. Calculate the Mach number, the velocity of the stream, and stagnation pressure. Assume perfect gas model with k=1.42. Solution This exactly the case discussed above in which the the ratio of mass flow rate to the area is given along with the stagnation temperature and static pressure. Utilizing equation (13.62) will provide the solution.  2  2 R T0 m ˙ 287 × 373 1 (13.VIII.a) = × = 2.676275 P2 A 200, 0002 0.001 According to Table 13.1 the Mach number is about M = 0.74 · · · (the exact number does not appear here demonstrate the simplicity of the solution). The Velocity can be obtained from the √ (13.VIII.b) U = M c = M kRT The only unknown the equation (13.VIII.b) is the temperature. However, the temperature can be obtained from knowing the Mach number with the “regular” table. Utilizing the regular table or Potto GDC one obtained.

13.4. ISENTROPIC FLOW

487 ρ ρ0

T T0

M

A A?

0.74000 0.89686 0.77169 1.0677

P P0

A×P A∗ ×P0

F F∗

0.69210 0.73898 0.54281

The temperature is then T = (287 + 300) × 0.89686 ∼ 526.45K ∼ 239.4◦ C

(13.VIII.c)

Hence the velocity is U = 0.74 ×

√

1.42 × 287 × 526.45 ∼ 342.76[m/sec]

(13.VIII.d)

In the same way the static pressure is  P P0 = P ∼ 2/0.692 ∼ 2.89[Bar] P0

(13.VIII.e)

The usage of Table 13.1 is only approximation and the exact value can be obtained utilizing Potto GDC. End Solution

Example 13.9: Calculate the Mach number for flow with given stagnation pressure of 2 [Bar] and 27◦ C. It is given that the mass flow rate is 1 [kg/sec] and the cross section area is 0.01[m2 ]. Assume that the specific heat ratios, k =1.4. Solution To solve this problem, the ratio 

A ∗ P0 AP

2

This mean that M

RT = P0 2



m ˙ A

RT P0 2

2


m ˙ 2 A

has to be found.

287 × 300 = 2000002



1 0.01

2

(13.IX.a)

∼ 0.021525

A ∗ P0 ∼ 0.1467. In the table it translate into AP T T0

ρ ρ0

A A?

0.08486 0.99856 0.99641 6.8487 End Solution

P P0

A×P A∗ ×P0

0.99497 6.8143

F F∗

2.8679

488

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Table -13.1. Fliegner’s number and other parameters as a function of Mach number

ρˆ



P0 A∗ AP

2

RT0 P2


m ˙ 2 A

1 Rρ0 P


m ˙ 2 A

1 Rρ0 2 T


m ˙ 2 A

M

Fn

0.00

1.4E−06

1.000

0.05

0.070106

1.000

0.00747

2.62E−05

0.00352

0.00351

0.10

0.14084

1.000

0.029920

0.000424

0.014268

0.014197

0.20

0.28677

1.001

0.12039

0.00707

0.060404

0.059212

0.21

0.30185

1.001

0.13284

0.00865

0.067111

0.065654

0.22

0.31703

1.001

0.14592

0.010476

0.074254

0.072487

0.23

0.33233

1.002

0.15963

0.012593

0.081847

0.079722

0.24

0.34775

1.002

0.17397

0.015027

0.089910

0.087372

0.25

0.36329

1.003

0.18896

0.017813

0.098460

0.095449

0.26

0.37896

1.003

0.20458

0.020986

0.10752

0.10397

0.27

0.39478

1.003

0.22085

0.024585

0.11710

0.11294

0.28

0.41073

1.004

0.23777

0.028651

0.12724

0.12239

0.29

0.42683

1.005

0.25535

0.033229

0.13796

0.13232

0.30

0.44309

1.005

0.27358

0.038365

0.14927

0.14276

0.31

0.45951

1.006

0.29247

0.044110

0.16121

0.15372

0.32

0.47609

1.007

0.31203

0.050518

0.17381

0.16522

0.33

0.49285

1.008

0.33226

0.057647

0.18709

0.17728

0.34

0.50978

1.009

0.35316

0.065557

0.20109

0.18992

0.35

0.52690

1.011

0.37474

0.074314

0.21584

0.20316

0.36

0.54422

1.012

0.39701

0.083989

0.23137

0.21703

0.37

0.56172

1.013

0.41997

0.094654

0.24773

0.23155

0.38

0.57944

1.015

0.44363

0.10639

0.26495

0.24674

0.39

0.59736

1.017

0.46798

0.11928

0.28307

0.26264

0.40

0.61550

1.019

0.49305

0.13342

0.30214

0.27926

0.41

0.63386

1.021

0.51882

0.14889

0.32220

0.29663

0.0

0.0

0.0

0.0

13.4. ISENTROPIC FLOW

489

Table -13.1. Fliegner’s number and other parameters as function of Mach number (continue)

M

Fn

ρˆ

0.42

0.65246

1.023

0.43

0.67129

0.44



P0 A∗ AP

2

RT0 P2


m ˙ 2 A

1 Rρ0 P


m ˙ 2 A

1 Rρ0 2 T


m ˙ 2 A

0.54531

0.16581

0.34330

0.31480

1.026

0.57253

0.18428

0.36550

0.33378

0.69036

1.028

0.60047

0.20442

0.38884

0.35361

0.45

0.70969

1.031

0.62915

0.22634

0.41338

0.37432

0.46

0.72927

1.035

0.65857

0.25018

0.43919

0.39596

0.47

0.74912

1.038

0.68875

0.27608

0.46633

0.41855

0.48

0.76924

1.042

0.71967

0.30418

0.49485

0.44215

0.49

0.78965

1.046

0.75136

0.33465

0.52485

0.46677

0.50

0.81034

1.050

0.78382

0.36764

0.55637

0.49249

0.51

0.83132

1.055

0.81706

0.40333

0.58952

0.51932

0.52

0.85261

1.060

0.85107

0.44192

0.62436

0.54733

0.53

0.87421

1.065

0.88588

0.48360

0.66098

0.57656

0.54

0.89613

1.071

0.92149

0.52858

0.69948

0.60706

0.55

0.91838

1.077

0.95791

0.57709

0.73995

0.63889

0.56

0.94096

1.083

0.99514

0.62936

0.78250

0.67210

0.57

0.96389

1.090

1.033

0.68565

0.82722

0.70675

0.58

0.98717

1.097

1.072

0.74624

0.87424

0.74290

0.59

1.011

1.105

1.112

0.81139

0.92366

0.78062

0.60

1.035

1.113

1.152

0.88142

0.97562

0.81996

0.61

1.059

1.122

1.194

0.95665

1.030

0.86101

0.62

1.084

1.131

1.236

1.037

1.088

0.90382

0.63

1.109

1.141

1.279

1.124

1.148

0.94848

0.64

1.135

1.151

1.323

1.217

1.212

0.99507

0.65

1.161

1.162

1.368

1.317

1.278

1.044

0.66

1.187

1.173

1.414

1.423

1.349

1.094

490

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Table -13.1. Fliegner’s number and other parameters as function of Mach number (continue)

M

Fn

ρˆ

0.67

1.214

1.185

0.68

1.241

1.198

0.69

1.269

0.70



P0 A∗ AP

1.461

2

RT0 P2


m ˙ 2 A

1 Rρ0 P


m ˙ 2 A

1 Rρ0 2 T


m ˙ 2 A

1.538

1.422

1.147

1.508

1.660

1.500

1.202

1.211

1.557

1.791

1.582

1.260

1.297

1.225

1.607

1.931

1.667

1.320

0.71

1.326

1.240

1.657

2.081

1.758

1.382

0.72

1.355

1.255

1.708

2.241

1.853

1.448

0.73

1.385

1.271

1.761

2.412

1.953

1.516

0.74

1.415

1.288

1.814

2.595

2.058

1.587

0.75

1.446

1.305

1.869

2.790

2.168

1.661

0.76

1.477

1.324

1.924

2.998

2.284

1.738

0.77

1.509

1.343

1.980

3.220

2.407

1.819

0.78

1.541

1.362

2.038

3.457

2.536

1.903

0.79

1.574

1.383

2.096

3.709

2.671

1.991

0.80

1.607

1.405

2.156

3.979

2.813

2.082

0.81

1.642

1.427

2.216

4.266

2.963

2.177

0.82

1.676

1.450

2.278

4.571

3.121

2.277

0.83

1.712

1.474

2.340

4.897

3.287

2.381

0.84

1.747

1.500

2.404

5.244

3.462

2.489

0.85

1.784

1.526

2.469

5.613

3.646

2.602

0.86

1.821

1.553

2.535

6.006

3.840

2.720

0.87

1.859

1.581

2.602

6.424

4.043

2.842

0.88

1.898

1.610

2.670

6.869

4.258

2.971

0.89

1.937

1.640

2.740

7.342

4.484

3.104

0.90

1.977

1.671

2.810

7.846

4.721

3.244

0.91

2.018

1.703

2.882

8.381

4.972

3.389

13.4. ISENTROPIC FLOW

491

Table -13.1. Fliegner’s number and other parameters as function of Mach number (continue)

M

Fn

ρˆ



P0 A∗ AP

0.92

2.059

1.736

2.955

0.93

2.101

1.771

3.029

0.94

2.144

1.806

3.105

0.95

2.188

1.843

0.96

2.233

0.97

2


m ˙ 2 A

RT0 P2

1 Rρ0 P


m ˙ 2 A

1 Rρ0 2 T


m ˙ 2 A

8.949

5.235

3.541

9.554

5.513

3.699

10.20

5.805

3.865

3.181

10.88

6.112

4.037

1.881

3.259

11.60

6.436

4.217

2.278

1.920

3.338

12.37

6.777

4.404

0.98

2.324

1.961

3.419

13.19

7.136

4.600

0.99

2.371

2.003

3.500

14.06

7.515

4.804

1.00

2.419

2.046

3.583

14.98

7.913

5.016

Example 13.10: A gas flows in the tube with mass flow rate of 0.1 [kg/sec] and tube cross section is 0.001[m2 ]. The temperature at chamber supplying the pressure to tube is 27◦ C. At some point the static pressure was measured to be 1.5[Bar]. Calculate for that point the Mach number, the velocity, and the stagnation pressure. Assume that the process is isentropic, k = 1.3, R = 287[j/kgK]. Solution The first thing that need to be done is to find the mass flow per area and it is m ˙ = 0.1/0.001 = 100.0[kg/sec/m2 ] A It can be noticed that the total temperature is 300K and the static pressure is 1.5[Bar]. It is fortunate that Potto-GDC exist and it can be just plug into it and it provide that M

T T0

ρ ρ0

A A?

0.17124 0.99562 0.98548 3.4757

P P0

A×P A∗ ×P0

0.98116 3.4102

F F∗

1.5392

The velocity can be calculated as √ √ U = M c = k R T M = 0.17 × 1.3 × 287 × 300× ∼ 56.87[m/sec]

492

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

The stagnation pressure is P0 =

P = 1.5/0.98116 = 1.5288[Bar] P/P0 End Solution

13.4.6

Isentropic Tables

Table -13.2. Isentropic Table k = 1.4 ρ ρ0

M

T T0

A A?

0.00

1.00000

1.00000

0.05

0.99950

0.99875

0.10

0.99800

0.99502

5.822

0.99303

5.781

2.443

0.20

0.99206

0.98028

2.964

0.97250

2.882

1.268

0.30

0.98232

0.95638

2.035

0.93947

1.912

0.89699

0.40

0.96899

0.92427

1.590

0.89561

1.424

0.72632

0.50

0.95238

0.88517

1.340

0.84302

1.130

0.63535

0.60

0.93284

0.84045

1.188

0.78400

0.93155

0.58377

0.70

0.91075

0.79158

1.094

0.72093

0.78896

0.55425

0.80

0.88652

0.73999

1.038

0.65602

0.68110

0.53807

0.90

0.86059

0.68704

1.009

0.59126

0.59650

0.53039

0.95

0.00328

1.061

1.002

1.044

0.95781

1.017

0.96

0.00206

1.049

1.001

1.035

0.96633

1.013

0.97

0.00113

1.036

1.001

1.026

0.97481

1.01

0.98

0.000495 1.024

1.0

1.017

0.98325

1.007

0.99

0.000121 1.012

1.0

1.008

0.99165

1.003

1.00

0.83333

0.63394

1.000

0.52828

0.52828

0.52828

1.1

0.80515

0.58170

1.008

0.46835

0.47207

0.52989

1.2

0.77640

0.53114

1.030

0.41238

0.42493

0.53399

1.3

0.74738

0.48290

1.066

0.36091

0.38484

0.53974

5.8E+5 11.59

P P0

1.0000 0.99825

A×P A∗ ×P0

F F∗

5.8E + 5

2.4E+5

11.57

4.838

13.4. ISENTROPIC FLOW

493

Table -13.2. Isentropic Table k=1.4 (continue)

M

T T0

ρ ρ0

A A?

P P0

A×P A∗ ×P0

F F∗

1.4

0.71839

0.43742

1.115

0.31424

0.35036

0.54655

1.5

0.68966

0.39498

1.176

0.27240

0.32039

0.55401

1.6

0.66138

0.35573

1.250

0.23527

0.29414

0.56182

1.7

0.63371

0.31969

1.338

0.20259

0.27099

0.56976

1.8

0.60680

0.28682

1.439

0.17404

0.25044

0.57768

1.9

0.58072

0.25699

1.555

0.14924

0.23211

0.58549

2.0

0.55556

0.23005

1.688

0.12780

0.21567

0.59309

2.5

0.44444

0.13169

2.637

0.058528

0.15432

0.62693

3.0

0.35714

0.076226

4.235

0.027224

0.11528

0.65326

3.5

0.28986

0.045233

6.790

0.013111

0.089018

0.67320

4.0

0.23810

0.027662 10.72

0.00659

0.070595

0.68830

4.5

0.19802

0.017449 16.56

0.00346

0.057227

0.69983

5.0

0.16667

0.011340 25.00

0.00189

0.047251

0.70876

5.5

0.14184

0.00758

36.87

0.00107

0.039628

0.71578

6.0

0.12195

0.00519

53.18

0.000633

0.033682

0.72136

6.5

0.10582

0.00364

75.13

0.000385

0.028962

0.72586

7.0

0.092593 0.00261

1.0E+2

0.000242

0.025156

0.72953

7.5

0.081633 0.00190

1.4E+2

0.000155

0.022046

0.73257

8.0

0.072464 0.00141

1.9E+2

0.000102

0.019473

0.73510

8.5

0.064725 0.00107

2.5E+2

6.90E−5

0.017321

0.73723

9.0

0.058140 0.000815

3.3E+2

4.74E−5

0.015504

0.73903

9.5

0.052493 0.000631

4.2E+2

3.31E−5

0.013957

0.74058

10.0

0.047619 0.000495

5.4E+2

2.36E−5

0.012628

0.74192

(Largest tables in the world can be found in Potto Gas Tables at www.potto.org)

494

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

13.4.7

The Impulse Function

One of the functions that is used in calculating the forces is the Impulse function. The Impulse function is denoted here as F , but in the literature some X − direction denote this function as I. To explain the motivation for using this definition consider the calculation of the net forces that acting on section shown in Figure (13.9). To calculate the net forces acting in the x–direction the momentum equation has to be Fig. -13.9. Schematic to explain the applied

significances of the Impulse function.

Fnet = m(U ˙ 2 − U1 ) + P2 A2 − P1 A1

(13.63)

The net force is denoted here as Fnet . The mass conservation also can be applied to our control volume m ˙ = ρ1 A1 U1 = ρ2 A2 U2

(13.64)

Combining equation (13.63) with equation (13.64) and by utilizing the identity in equation (13.48) results in Fnet = kP2 A2 M2 2 − kP1 A1 M1 2 + P2 A2 − P1 A1

(13.65)

Rearranging equation (13.65) and dividing it by P0 A∗ results in f (M2 )

f (M1 )

f (M1 ) 2) z }| { z f (M z }| { }| }|
{ P1 A1 z
{ P2 A 2 Fnet 2 2 = 1 + kM − 1 + kM 2 1 P0 A ∗ P0 A ∗ P0 A ∗

(13.66)

Examining equation (13.66) shows that the right hand side is only a function of Mach number and specific heat ratio, k. Hence, if the right hand side is only a function of the Mach number and k than the left hand side must be function of only the same parameters, M and k. Defining a function that depends only on the Mach number creates the convenience for calculating the net forces acting on any device. Thus, defining the Impulse function as
F = P A 1 + kM2 2 (13.67) In the Impulse function when F (M = 1) is denoted as F ∗ F ∗ = P ∗ A∗ (1 + k)

(13.68)

The ratio of the Impulse function is defined as F P1 A1 1 + kM1 = ∗ ∗ ∗ F P A (1 + k)

2




=

1 P∗ P0 |{z} k 2 ( k+1 ) k−1

see function (13.66) z }| {
P1 A 1 1 2 1 + kM1 ∗ P0 A (1 + k)

(13.69)

13.4. ISENTROPIC FLOW

495

This ratio is different only in a coefficient from the ratio defined in equation (13.66) which makes the ratio a function of k and the Mach number. Hence, the net force is Fnet

   k  k + 1 k−1 F2 F1 = P0 A (1 + k) − ∗ 2 F∗ F ∗

(13.70)

To demonstrate the usefulness of the this function consider a simple situation of the flow through a converging nozzle. Example 13.11: 1

Consider a flow of gas into a converging nozzle with a mass flow rate of 1[kg/sec] and the entrance area is 0.009[m2 ] and the exit area is 0.003[m2 ]. The stagnation temperature is 400K and the pressure at point 2 was measured as 5[Bar]. Calculate the net force acting on the nozzle and pressure at point 1.

2 m ˙ = 1[kg/sec] A1 = 0.009[m2]

A2 = 0.003[m2] P2 = 50[Bar]

T0 = 400K

Fig. -13.10. Schematic of a flow of a compressible substance (gas) through a converging nozzle for example (13.11)

Solution

The solution is obtained by getting the data for the Mach number. To obtained the Mach number, the ratio of P1 A1 /A∗ P0 is needed to be calculated. The denominator is needed to be determined to obtain this ratio. Utilizing Fliegner’s equation (13.57), provides the following √ √ m ˙ RT 1.0 × 400 × 287 ∗ A P0 = = ∼ 70061.76[N ] 0.058 0.058 and A2 P 2 500000 × 0.003 ∼ 2.1 = A ? P0 70061.76 M

ρ ρ0

T T0

A A?

0.27353 0.98526 0.96355 2.2121 With the area ratio of

A A?

P P0

A×P A∗ ×P0

0.94934 2.1000

F F∗

0.96666

= 2.2121 the area ratio of at point 1 can be calculated.

A1 0.009 A2 A1 = ? = 2.2121 × = 5.2227 ? A A A2 0.003 And utilizing again Potto-GDC provides

496

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL M

T T0

ρ ρ0

A A?

0.11164 0.99751 0.99380 5.2227

P P0

A×P A∗ ×P0

0.99132 5.1774

F F∗

2.1949

The pressure at point 1 is P1 = P 2

P0 P1 = 5.0 × 0.94934/0.99380 ∼ 4.776[Bar] P2 P0

The net force is obtained by utilizing equation (13.70)

Fnet

   k  F1 P0 A ∗ k + 1 k−1 F2 − ? = P2 A 2 (1 + k) P2 A 2 2 F? F 1 = 500000 × × 2.4 × 1.23.5 × (2.1949 − 0.96666) ∼ 614[kN ] 2.1 End Solution

13.5 Normal Shock In this section the relationships between the two ρx c.v. flow sides of normal shock are presented. In this discusdirection ρy P y Px sion, the flow is assumed to be in a steady state, Ty Tx and the thickness of the shock is assumed to be very small. A shock can occur in at least two different mechanisms. The first is when a large differFig. -13.11. A shock wave inside a ence (above a small minimum value) between the tube, but it can also be viewed as a two sides of a membrane, and when the membrane one–dimensional shock wave. bursts (see the discussion about the shock tube). Of course, the shock travels from the high pressure to the low pressure side. The second is when many sound waves “run into” each other and accumulate (some refer to it as “coalescing”) into a large difference, which is the shock wave. In fact, the sound wave can be viewed as an extremely weak shock. In the speed of sound analysis, it was assumed the medium is continuous, without any abrupt changes. This assumption is no longer valid in the case of a shock. Here, the relationship for a perfect gas is constructed. In Figure 13.11 a control volume for this analysis is shown, and the gas flows from left to right. The conditions, to the left and to the right of the shock, are assumed to be uniform7 . The conditions to the right of the shock wave are uniform, but different from the left side. The transition in the shock is abrupt and in a very narrow width. Therefore, the increase of the entropy is fundamental to the phenomenon and the understanding of it. 7 Clearly the change in the shock is so significant compared to the changes in medium before and after the shock that the changes in the mediums (flow) can be considered uniform.

13.5. NORMAL SHOCK

497

It is further assumed that there is no friction or heat loss at the shock (because the heat transfer is negligible due to the fact that it occurs on a relatively small surface). It is customary in this field to denote x as the upstream condition and y as the downstream condition. The mass flow rate is constant from the two sides of the shock and therefore the mass balance is reduced to ρx Ux = ρy Uy

(13.71)

In a shock wave, the momentum is the quantity that remains constant because there are no external forces. Thus, it can be written that
Px − Py = ρ x U y 2 − ρ y U x 2 (13.72)

The process is adiabatic, or nearly adiabatic, and therefore the energy equation can be written as Cp Tx +

Uy 2 Ux 2 = Cp Ty + 2 2

(13.73)

The equation of state for perfect gas reads P = ρRT

(13.74)

If the conditions upstream are known, then there are four unknown conditions downstream. A system of four unknowns and four equations is solvable. Nevertheless, one can note that there are two solutions because of the quadratic of equation (13.73). These two possible solutions refer to the direction of the flow. Physics dictates that there is only one possible solution. One cannot deduce the direction of the flow from the pressure on both sides of the shock wave. The only tool that brings us to the direction of the flow is the second law of thermodynamics. This law dictates the direction of the flow, and as it will be shown, the gas flows from a supersonic flow to a subsonic flow. Mathematically, the second law is expressed by the entropy. For the adiabatic process, the entropy must increase. In mathematical terms, it can be written as follows: sy − sx > 0

(13.75)

Note that the greater–equal signs were not used. The reason is that the process is irreversible, and therefore no equality can exist. Mathematically, the parameters are P, T, U, and ρ, which are needed to be solved. For ideal gas, equation (13.75) is   Ty Py ln − (k − 1) >0 (13.76) Tx Px It can also be noticed that entropy, s, can be expressed as a function of the other parameters. These equations can be viewed as two different subsets of equations. The first set is the energy, continuity, and state equations, and the second set is the momentum, continuity, and state equations. The solution of every set of these equations

498

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

produces one additional degree of freedom, which will produce a range of possible solutions. Thus, one can have a whole range of solutions. In the first case, the energy equation is used, producing various resistance to the flow. This case is called Fanno flow, and Section 13.7 deals extensively with this topic. Instead of solving all the equations that were presented, one can solve only four (4) equations (including the second law), which will require additional parameters. If the energy, continuity, and state equations are solved for the arbitrary value of the Ty , a parabola in the T − s diagram will be obtained. On the other hand, when the momentum equation is solved instead of the energy equation, the degree of freedom is now energy, i.e., the energy amount “added” to the shock. This situation is similar to a frictionless flow with the addition of heat, and this flow is known as Rayleigh flow. This flow is dealt with in greater detail in Section (13.9). Since the shock has no heat transfer (a special case of Rayleigh flow) and there isn’t essentially any momentum transfer (a special case of Fanno flow), the intersection of these two curves is what really happened in the shock. The entropy increases from point x to point y.

13.5.1

Solution of the Governing Equations

Equations (13.71), (13.72), and (13.73) can be converted into a dimensionless form. The reason that dimensionless forms are heavily used in this book is because by doing so it simplifies and clarifies the solution. It can also be noted that in many cases the dimensionless equations set is more easily solved. From the continuity equation (13.71) substituting for density, ρ, the equation of state yields Py Px Ux = Uy R Tx R Ty

(13.77)

Squaring equation (13.77) results in Px 2 Py 2 2 U Uy 2 = x 2 R2 Tx R2 Ty 2

(13.78)

Multiplying the two sides by the ratio of the specific heat, k, provides a way to obtain the speed of sound definition/equation for perfect gas, c2 = k R T to be used for the Mach number definition, as follows: Py 2 Px 2 Ux 2 = Uy 2 Tx k R Tx Ty k R Ty | {z } | {z } cx 2

(13.79)

cy 2

Note that the speed of sound is different on the sides of the shock. Utilizing the definition of Mach number results in Px 2 Py 2 Mx 2 = My 2 Tx Ty

(13.80)

13.5. NORMAL SHOCK

499

Rearranging equation (13.80) results in  2  2 Ty Py My = Tx Px Mx

(13.81)

Energy equation (13.73) can be converted to a dimensionless form which can be expressed as     k−1 k−1 2 2 Ty 1 + My = Tx 1 + Mx (13.82) 2 2 It can also be observed that equation (13.82) means that the stagnation temperature is the same, T0y = T0x . Under the perfect gas model, ρ U 2 is identical to k P M 2 because M2

z }| {

ρ

z}|{ 2  P  2  U  k R T = k P M2 ρU =   RT k |R {zT}

(13.83)

c2

Using the identity (13.83) transforms the momentum equation (13.72) into Px + k P x M x 2 = Py + k P y M y 2

(13.84)

Rearranging equation (13.84) yields 1 + k Mx 2 Py = Px 1 + k My 2

(13.85)

The pressure ratio in equation (13.85) can be interpreted as the loss of the static pressure. The loss of the total pressure ratio can be expressed by utilizing the relationship between the pressure and total pressure (see equation (13.27)) as

P0y P0x

 k k−1 k−1 Py 1 + My 2 2 =   k k−1 2 k−1 Px 1 + Mx 2 

(13.86)

The relationship between Mx and My is needed to be solved from the above set of equations. This relationship can be obtained from the combination of mass, momentum, and energy equations. From equation (13.82) (energy) and equation (13.81) (mass) the temperature ratio can be eliminated. 

Py M y Px M x

2

k−1 Mx 2 2 = k−1 1+ My 2 2 1+

(13.87)

500

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Combining the results of (13.87) with equation (13.85) results in 

1 + k Mx 2 1 + k My 2

2

=



Mx My

 2 1 + k − 1 Mx 2 2 k−1 1+ My 2 2

(13.88)

Equation (13.88) is a symmetrical equation in the sense that if My is substituted with Mx and Mx substituted with My the equation remains the same. Thus, one solution is My = Mx

(13.89)

It can be observed that equation (13.88) is biquadratic. According to the Gauss Biquadratic Reciprocity Theorem this kind of equation has a real solution in a certain range8 which will be discussed later. The solution can be obtained by rewriting equation (13.88) as a polynomial (fourth order). It is also possible to cross–multiply equation
(13.88) and divide it by Mx 2 − My 2 results in 1+


k−1 My 2 + My 2 − k M y 2 My 2 = 0 2

(13.90)

Equation (13.90) becomes

Shock Solution My 2 =

Mx 2 +

2 k−1

(13.91)

2k Mx 2 − 1 k−1

The first solution (13.89) is the trivial solution in which the two sides are identical and no shock wave occurs. Clearly, in this case, the pressure and the temperature from both sides of the nonexistent shock are the same, i.e. Tx = Ty , Px = Py . The second solution is where the shock wave occurs. The pressure ratio between the two sides can now be as a function of only a single Mach number, for example, Mx . Utilizing equation (13.85) and equation (13.91) provides the pressure ratio as only a function of the upstream Mach number as Py 2k k−1 = Mx 2 − Px k+1 k+1 Shock Pressure Ratio
Py 2k =1+ Mx 2 − 1 Px k+1

or

(13.92)

8 Ireland, K. and Rosen, M. ”Cubic and Biquadratic Reciprocity.” Ch. 9 in A Classical Introduction to Modern Number Theory, 2nd ed. New York: Springer-Verlag, pp. 108-137, 1990.

13.5. NORMAL SHOCK

501

The density and upstream Mach number relationship can be obtained in the same fashion to became Shock Density Ratio ρy Ux (k + 1)Mx 2 = = ρx Uy 2 + (k − 1)Mx 2

(13.93)

The fact that the pressure ratio is a function of the upstream Mach number, Mx , provides additional way of obtaining an additional useful relationship. And the temperature ratio, as a function of pressure ratio, is transformed into Shock Temperature Ratio   k + 1 Py   +  Ty Py   k − 1 Px  = k + 1 Py  Tx Px  1+ k − 1 Px

(13.94)

In the same way, the relationship between the density ratio and pressure ratio is Shock P − ρ    Py k+1 1+ ρx k−1 Px    =  Py k+1 ρy + k−1 Px

(13.95)

which is associated with the shock wave. 13.5.1.1

The Star Conditions

The speed of sound at the critical condition can also be a good reference velocity. The speed of sound at that velocity is √ c∗ = k R T ∗ (13.96) In the same manner, an additional Mach number can be defined as M∗ =

13.5.2

U c∗

(13.97)

Prandtl’s Condition

It can be easily observed that the temperature from both sides of the shock wave is discontinuous. Therefore, the speed of sound is different in these adjoining mediums. It is therefore convenient to define the star Mach number that will be independent of the specific Mach number (independent of the temperature).

502

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Shock Wave relationship My and P0y/P0x as a function of Mx 1 0.9 0.8

My

0.7

P0y/P0x

My

0.6 0.5 0.4 0.3 0.2 0.1 0

1 2 3 Fri Jun 18 15:47:34 2004

4

5

6

7

8

9

10

Mx

Fig. -13.12. The exit Mach number and the stagnation pressure ratio as a function of upstream Mach number.

13.5. NORMAL SHOCK

503

M∗ =

c U c U = ∗ = ∗M ∗ c c c c

(13.98)

The jump condition across the shock must satisfy the constant energy. c2 U2 c∗ 2 c∗ 2 k + 1 ∗2 + = + = c k−1 2 k−1 2 2 (k − 1)

(13.99)

Dividing the mass equation by the momentum equation and combining it with the perfect gas model yields c1 2 c2 2 + U1 = + U2 k U1 k U2

(13.100)

Combining equation (13.99) and (13.100) results in     1 k + 1 ∗2 k − 1 1 k + 1 ∗2 k − 1 c − U1 + U1 = c − U2 + U2 k U1 2 2 k U2 2 2

(13.101)

After rearranging and dividing equation (13.101) the following can be obtained: U1 U2 = c∗ 2

(13.102)

M ∗ 1 M ∗ 2 = c∗ 2

(13.103)

or in a dimensionless form

13.5.3

Operating Equations and Analysis

In Figure 13.12, the Mach number after the shock, My , and the ratio of the total pressure, P0y /P0x , are plotted as a function of the entrance Mach number. The working equations were presented earlier. Note that the My has a minimum value which depends on the specific heat ratio. It can be noticed that the density ratio (velocity ratio) also has a finite value regardless of the upstream Mach number. The typical situations in which these equations can be used also include the moving shocks. The equations should be used with the Mach number (upstream or downstream) for a given pressure ratio or density ratio (velocity ratio). This kind of equations requires examining Table 13.3 for k = 1.4 or utilizing Potto-GDC for for value of the specific heat ratio. Finding the Mach number for a pressure ratio of 8.30879 and k = 1.32 and is only a few mouse clicks away from the following table. To illustrate the use of the above equations, an example is proShock Wave relationship Py/Py, ρy/ρx and Ty/Tx as a function of Mx vided. 120.0

Example 13.12: Air flows with a Mach number of

110.0 100.0

Py/Px

90.0

Ty/Tx

80.0

ρy/ρx

70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0

1 2 3 Fri Jun 18 15:48:25 2004

4

5

6

7

8

9

10

Mx

Fig. -13.13. The ratios of the static properties of

504

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Mx = 3, at a pressure of 0.5 [bar] and a temperature of 0◦ C goes through a normal shock. Calculate the temperature, pressure, total pressure, and velocity downstream of the shock. Assume that k = 1.4. Solution Analysis: First, the known information are Mx = 3, Px = 1.5[bar] and Tx = 273K. Using these data, the total pressure can be obtained (through an isentropic relationship in Table (13.2), i.e., P0x is known). Also with the temperature, Tx , the velocity can readily be calculated. The relationship that was calculated will be utilized to obtain the ratios for the downstream x = 0.0272237 =⇒ P0x = 1.5/0.0272237 = 55.1[bar] of the normal shock. PP0x p

cx =

√

1.4 × 287 × 273 = 331.2m/sec

My

Ty Tx

ρy ρx

0.47519

2.6790

3.8571

Mx 3.0000

k R Tx =

Py Px

10.3333

P0y P0 x

0.32834

Ux = Mx × cx = 3 × 331.2 = 993.6[m/sec] Now the velocity downstream is determined by the inverse ratio of ρy /ρx = Ux /Uy = 3.85714. Uy = 993.6/3.85714 = 257.6[m/sec]

P0y =



P0y P0x



× P0x = 0.32834 × 55.1[bar] = 18.09[bar] End Solution

When the upstream Mach number becomes very large, the downstream Mach number (see equation (13.91)) is limited by

My 2 =

* ∼0 2  1+  (k − 1)Mx 2  2k 1 − k − 1 Mx 2

∼0

=

k−1 2k

(13.104)

13.5. NORMAL SHOCK

505

This result is shown in Figure 13.12. The limits of the pressure ratio can be obtained by looking at equation (13.85) and by utilizing the limit that was obtained in equation (13.104).

13.5.4

The Moving Shocks

In some situations, the shock wave is not stationary. This kind of situation arises in many industrial applications. For example, when a valve is suddenly 9 closed and a shock propagates upstream. On the other extreme, when a valve is suddenly opened or a membrane is ruptured, a shock occurs and propagates downstream (the opposite direction of the previous case). In addition to (partially) closing or (partially) opening of value, the rigid body (not so rigid body) movement creates shocks. In some industrial applications, a liquid (metal) is pushed in two rapid stages to a cavity through a pipe system. This liquid (metal) is pushing gas (mostly) air, which creates two shock stages. The moving shock is observed by daily as hearing sound wave are moving shocks. As a general rule, the moving shock can move downstream or upstream. The source of the shock creation, either due to the static device operation like valve operating/closing or due to moving object, is relevant to analysis but it effects the boundary conditions. This creation difference while creates the same moving shock it creates different questions and hence in some situations complicate the calculations. The most general case which this section will be dealing with is the partially open or close wave. A brief discussion on the such case (partially close/open but due the moving object) will be presented. There are more general cases where the moving shocks are created which include a change in the physical properties, but this book will not deal with them at this stage. The reluctance to deal with the most general case is due to fact it is highly specialized and complicated even beyond early graduate students level. In these changes (of opening a valve and closing a valve on the other side) create situations in which different shocks are moving in the tube. The general case is where two shocks collide into one shock and moves upstream or downstream is the general case. A specific example is common in die–casting: after the first shock moves a second shock is created in which its velocity is dictated by the upstream and downstream velocities.

U′y Us Px < Py

c.v. U′x ρ y Py T y

(a) Stationary coordinates.

Us −U′y




U=0 Px < Py

c.v.
Us −U′x ρ y Py T y

(b) Moving coordinates.

Fig. -13.14. Comparison between stationary and moving coordinates for the moving shock.

In cases where the shock velocity can be approximated as a constant (in the 9 It

will be explained using dimensional analysis what is suddenly open.

506

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

majority of cases) or as near constant, the previous analysis, equations, and the tools developed in this chapter can be employed. The problem can be reduced to the previously studied shock, i.e., to the stationary case when the coordinates are attached to the shock front. In such a case, the steady state is obtained in the moving control value. For this analysis, the coordinates move with the shock. Here, the prime 0 denotes the values of the static coordinates. Note that this notation is contrary to the conventional notation found in the literature. The reason for the deviation is that this choice reduces the programing work (especially for object–oriented programing like C++). An observer moving with the shock will notice that the pressure in the shock sides is 0

Px = Px

0

Py = Py

(13.105)

The temperatures measured by the observer are 0

Tx = Tx

0

Ty = Ty

(13.106)

Assuming that the shock is moving to the right, (refer to Figure 13.14) the velocity measured by the observer is Ux = Us − Ux

0

(13.107)

Where Us is the shock velocity which is moving to the right. The “downstream” velocity is 0

Uy = Us − Uy

(13.108)

The speed of sound on both sides of the shock depends only on the temperature and it is assumed to be constant. The upstream prime Mach number can be defined as 0

Mx =

Us Us − Ux = − Mx = Msx − Mx cx cx

(13.109)

It can be noted that the additional definition was introduced for the shock upstream Mach number, Msx = Ucxs . The downstream prime Mach number can be expressed as 0

My =

Us − Uy Us = − My = Msy − My cy cy

(13.110)

Similar to the previous case, an additional definition was introduced for the shock downstream Mach number, Msy . The relationship between the two new shock Mach numbers is

Msx

Us cy Us = cx cx cy r Ty = Msy Tx

(13.111)

13.5. NORMAL SHOCK

507

The “upstream” stagnation temperature of the fluid is Shock Stagnation Temperature   k−1 2 Mx T0x = Tx 1 + 2

(13.112)

and the “upstream” prime stagnation pressure is P0x

 k  k−1 k−1 2 Mx = Px 1 + 2

(13.113)

The same can be said for the “downstream” side of the shock. The difference between the stagnation temperature is in the moving coordinates T0y − T0x = 0

13.5.5

(13.114)

Shock or Wave Drag Result from a Moving Shock

It can be shown that there is no shock drag stationary lines at the speed of the object in stationary shockfor more information see “Fundamentals of Compressible Flow, Potto Project, Bar-Meir any verstion”.. However, moving U2 6= 0 U1 = 0 ρ2 object ρ1 the shock or wave drag is very significant so A1 A2 much so that at one point it was considered P1 P2 the sound barrier. Consider the Figure 13.15 where the stream lines are moving with the obstream lines ject speed. The other boundaries are stationary but the velocity at right boundary is not Fig. -13.15. The diagram that reexplains zero. The same arguments, as discussed be- the shock drag effect of a moving shock. fore in the stationary case, are applied. What is different in the present case (as oppose to the stationary shock), one side has increase the momentum of the control volume. This increase momentum in the control volume causes the shock drag. In way, it can be view as continuous acceleration of the gas around the body from zero. Note this drag is only applicable to a moving shock (unsteady shock). The moving shock is either results from a body that moves in gas or from a sudden imposed boundary like close or open valve10 . In the first case, the forces or energies flow from body to gas and therefor there is a need for large force to accelerate the gas over extremely short distance (shock thickness). In the second case, the gas contains the energy (as high pressure, for example in the open valve case) and the energy potential is lost in the shock process (like shock drag). 10 According to my son, the difference between these two cases is the direction of the information. Both case there essentially bodies, however, in one the information flows from inside the field to the boundary while the other case it is the opposite.

508

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Fig. -13.16. The diagram for the common explanation for shock or wave drag effect a shock. Please notice the strange notations (e.g. V and not U) and they result from a verbatim copy.

For some strange reasons, this topic has several misconceptions that even appear in many popular and good textbooks11 . Consider the following example taken from such a book. Example 13.13: A book (see Figure 13.16) explains the shock drag is based on the following rational: The body is moving in a stationary frictionless fluid under one–dimensional flow. The left plane is moving with body at the same speed. The second plane is located “downstream from the body where the gas has expanded isotropically (after the shock wave) to the upstream static pressure.” The bottom and upper stream line close the control volume. Since the pressure is the same on the both planes there is no unbalanced pressure forces. However, there is a change in the momentum in the flow direction because (U1 > U2 ). The force is acting on the body. There several mistakes in this explanation including the drawing. Explain what is wrong in this description (do not describe the error results from oblique shock). Solution Neglecting the mistake around the contact of the stream lines with the oblique shock(see for retouch in the oblique chapter), the control volume suggested is stretched with time. However, the common explanation fall to notice that when the isentropic explanation occurs the width of the area change. Thus, the simple explanation in a change only in momentum (velocity) is not appropriate. Moreover, in an expanding control volume this simple explanation is not appropriate. Notice that the relative velocity at the front of the control volume U1 is actually zero. Hence, the claim of U1 > U2 is actually the opposite, U1 < U2 . End Solution

11 Similar

situation exist in the surface tension area.

13.5. NORMAL SHOCK

13.5.6

509

Qualitative questions

1. In the analysis of the maximum temperature in the shock tube, it was assumed that process is isentropic. If this assumption is not correct would the maximum temperature obtained is increased or decreased? 2. In the analysis of the maximum temperature in the shock wave it was assumed that process is isentropic. Clearly, this assumption is violated when there are shock waves. In that cases, what is the reasoning behind use this assumption any why?

13.5.7

Tables of Normal Shocks, k = 1.4 Ideal Gas

Table -13.3. The shock wave table for k = 1.4

My

Ty Tx

ρy ρx

Py Px

P0y P0x

1.00

1.00000

1.00000

1.00000

1.00000

1.00000

1.05

0.95313

1.03284

1.08398

1.11958

0.99985

1.10

0.91177

1.06494

1.16908

1.24500

0.99893

1.15

0.87502

1.09658

1.25504

1.37625

0.99669

1.20

0.84217

1.12799

1.34161

1.51333

0.99280

1.25

0.81264

1.15938

1.42857

1.65625

0.98706

1.30

0.78596

1.19087

1.51570

1.80500

0.97937

1.35

0.76175

1.22261

1.60278

1.95958

0.96974

1.40

0.73971

1.25469

1.68966

2.12000

0.95819

1.45

0.71956

1.28720

1.77614

2.28625

0.94484

1.50

0.70109

1.32022

1.86207

2.45833

0.92979

1.55

0.68410

1.35379

1.94732

2.63625

0.91319

1.60

0.66844

1.38797

2.03175

2.82000

0.89520

1.65

0.65396

1.42280

2.11525

3.00958

0.87599

1.70

0.64054

1.45833

2.19772

3.20500

0.85572

1.75

0.62809

1.49458

2.27907

3.40625

0.83457

1.80

0.61650

1.53158

2.35922

3.61333

0.81268

Mx

510

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Table -13.3. The shock wave table for k = 1.4 (continue)

My

Ty Tx

ρy ρx

Py Px

P0y P0x

1.85

0.60570

1.56935

2.43811

3.82625

0.79023

1.90

0.59562

1.60792

2.51568

4.04500

0.76736

1.95

0.58618

1.64729

2.59188

4.26958

0.74420

2.00

0.57735

1.68750

2.66667

4.50000

0.72087

2.05

0.56906

1.72855

2.74002

4.73625

0.69751

2.10

0.56128

1.77045

2.81190

4.97833

0.67420

2.15

0.55395

1.81322

2.88231

5.22625

0.65105

2.20

0.54706

1.85686

2.95122

5.48000

0.62814

2.25

0.54055

1.90138

3.01863

5.73958

0.60553

2.30

0.53441

1.94680

3.08455

6.00500

0.58329

2.35

0.52861

1.99311

3.14897

6.27625

0.56148

2.40

0.52312

2.04033

3.21190

6.55333

0.54014

2.45

0.51792

2.08846

3.27335

6.83625

0.51931

2.50

0.51299

2.13750

3.33333

7.12500

0.49901

2.75

0.49181

2.39657

3.61194

8.65625

0.40623

3.00

0.47519

2.67901

3.85714

10.33333

0.32834

3.25

0.46192

2.98511

4.07229

12.15625

0.26451

3.50

0.45115

3.31505

4.26087

14.12500

0.21295

3.75

0.44231

3.66894

4.42623

16.23958

0.17166

4.00

0.43496

4.04688

4.57143

18.50000

0.13876

4.25

0.42878

4.44891

4.69919

20.90625

0.11256

4.50

0.42355

4.87509

4.81188

23.45833

0.09170

4.75

0.41908

5.32544

4.91156

26.15625

0.07505

5.00

0.41523

5.80000

5.00000

29.00000

0.06172

5.25

0.41189

6.29878

5.07869

31.98958

0.05100

Mx

13.6. ISOTHERMAL FLOW

511

Table -13.3. The shock wave table for k = 1.4 (continue)

My

Ty Tx

ρy ρx

5.50

0.40897

6.82180

5.14894

35.12500

0.04236

5.75

0.40642

7.36906

5.21182

38.40625

0.03536

6.00

0.40416

7.94059

5.26829

41.83333

0.02965

6.25

0.40216

8.53637

5.31915

45.40625

0.02498

6.50

0.40038

9.15643

5.36508

49.12500

0.02115

6.75

0.39879

9.80077

5.40667

52.98958

0.01798

7.00

0.39736

10.46939

5.44444

57.00000

0.01535

7.25

0.39607

11.16229

5.47883

61.15625

0.01316

7.50

0.39491

11.87948

5.51020

65.45833

0.01133

7.75

0.39385

12.62095

5.53890

69.90625

0.00979

8.00

0.39289

13.38672

5.56522

74.50000

0.00849

8.25

0.39201

14.17678

5.58939

79.23958

0.00739

8.50

0.39121

14.99113

5.61165

84.12500

0.00645

8.75

0.39048

15.82978

5.63218

89.15625

0.00565

9.00

0.38980

16.69273

5.65116

94.33333

0.00496

9.25

0.38918

17.57997

5.66874

99.65625

0.00437

9.50

0.38860

18.49152

5.68504

105.12500

0.00387

9.75

0.38807

19.42736

5.70019

110.73958

0.00343

10.00

0.38758

20.38750

5.71429

116.50000

0.00304

Mx

Py Px

P0y P0x

13.6 Isothermal Flow In this section a model dealing with gas that flows through a long tube is described. This model has a applicability to situations which occur in a relatively long distance and where heat transfer is relatively rapid so that the temperature can be treated, for engineering purposes, as a constant. For example, this model is applicable when a natural gas flows over several hundreds of meters. Such situations are common in large cities in U.S.A. where natural gas is used for heating. It is more predominant (more applicable) in situations where the gas is pumped over a length of kilometers.

512

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

w The high speed of the gas is obρ flow ρ + ∆ρ tained or explained by the combination of c.v. direction P P + ∆P o heat transfer and the friction to the flow. T (M) T + ∆T (M + ∆M) For a long pipe, the pressure difference reU + ∆U U duces the density of the gas. For instance, w in a perfect gas, the density is inverse of the pressure (it has to be kept in mind that Fig. -13.17. Control volume for isothermal flow. the gas undergoes an isothermal process.). To maintain conservation of mass, the velocity increases inversely to the pressure. At critical point the velocity reaches the speed of sound at the exit and hence the flow will be choked12 .

13.6.1

The Control Volume Analysis/Governing equations

Figure 13.17 describes the flow of gas from the left to the right. The heat transfer up stream (or down stream) is assumed to be negligible. Hence, the energy equation can be written as the following: U2 dQ = cp dT + d = cp dT0 m ˙ 2

(13.115)

The momentum equation is written as the following −A dP − τw dAwetted area = m ˙ dU

(13.116)

where A is the cross section area (it doesn’t have to be a perfect circle; a close enough shape is sufficient.). The shear stress is the force per area that acts on the fluid by the tube wall. The Awetted area is the area that shear stress acts on. The second law of thermodynamics reads s2 − s1 T2 k − 1 P2 = ln − ln Cp T1 k P1

(13.117)

The mass conservation is reduced to m ˙ = constant = ρ U A

(13.118)

Again it is assumed that the gas is a perfect gas and therefore, equation of state is expressed as the following: P = ρRT

(13.119)

√ explanation is not correct as it will be shown later on. Close to the critical point (about, 1/ k, the heat transfer, is relatively high and the isothermal flow model is not valid anymore. Therefore, the study of the isothermal flow above this point is only an academic discussion but also provides the upper limit for Fanno Flow. 12 This

13.6. ISOTHERMAL FLOW

13.6.2

513

Dimensionless Representation

In this section the equations are transformed into the dimensionless form and presented as such. First it must be recalled that the temperature is constant and therefore, equation of state reads dP dρ = P ρ

(13.120)

It is convenient to define a hydraulic diameter DH =

4 × Cross Section Area wetted perimeter

(13.121)

The Fanning friction factor13 is introduced, this factor is a dimensionless friction factor sometimes referred to as the friction coefficient as τw f= 1 2 (13.122) ρU 2 Substituting equation (13.122) into momentum equation (13.116) yields 4 dx f −dP − DH



1 ρ U2 2



m ˙ A z}|{ = ρ U dU

(13.123)

Rearranging equation (13.123) and using the identify for perfect gas M 2 = ρU 2 /kP yields:   dP 4 f dx k P M 2 k P M 2 dU − − = (13.124) P DH 2 U The pressure, P as a function of the Mach number has to substitute along with velocity, U as U2 = k R TM2

(13.125)

Differentiation of equation (13.125) yields d(U 2 ) = k R M 2 dT + T d(M 2 ) d(M 2 ) d(U 2 ) dT = − 2 M U2 T




(13.126)

(13.127)

It can be noticed that dT = 0 for isothermal process and therefore d(M 2 ) d(U 2 ) 2U dU 2dU = = = 2 2 2 M U U U

(13.128)

13 It should be noted that Fanning factor based on hydraulic radius, instead of diameter friction equation, thus “Fanning f” values are only 1/4th of “Darcy f” values.

514

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

The dimensionalization of the mass conservation equation yields dρ d(U 2 ) dρ dU dρ 2 U dU = =0 + = + + ρ U ρ 2U 2 ρ 2 U2

(13.129)

Differentiation of the isotropic (stagnation) relationship of the pressure (13.27) yields 

 k M2 dP0 dP   dM 2 2 = + k − 1 2  M2 P0 P 1+ M 2 Differentiation of equation (13.25) yields:   k−1 2 k−1 dT0 = dT 1 + M dM 2 +T 2 2

(13.130)

(13.131)

Notice that dT0 6= 0 in an isothermal flow. There is no change in the actual temperature of the flow but the stagnation temperature increases or decreases depending on the Mach number (supersonic flow of subsonic flow). Substituting T for equation (13.131) yields: k−1 T0 d M2 M2 2  dT0 =  k − 1 2 M2 1+ M 2

(13.132)

Rearranging equation (13.132) yields dT0 = T0

(k − 1) M 2 dM 2   k−1 M2 2 1+ 2

(13.133)

By utilizing the momentum equation it is possible to obtain a relation between the pressure and density. Recalling that an isothermal flow (dT = 0) and combining it with perfect gas model yields dρ dP = P ρ

(13.134)

From the continuity equation (see equation (13.128)) leads dM 2 2dU = M2 U

(13.135)

The four equations momentum, continuity (mass), energy, state are described above. There are 4 unknowns (M, T, P, ρ)14 and with these four equations the solution 14 Assuming

the upstream variables are known.

13.6. ISOTHERMAL FLOW

515

is attainable. One can notice that there are two possible solutions (because of the square power). These different solutions are supersonic and subsonic solution. fL The distance friction, t 4 D , is selected as the choice for the independent variable. Thus, the equations need to be obtained as a function of 4fDL . The density is eliminated from equation (13.129) when combined with equation (13.134) to become dP dU =− P U

(13.136)

After substituting the velocity (13.136) into equation (13.124), one can obtain   dP 4 f dx k P M 2 dP − − = k P M2 (13.137) P DH 2 P Equation (13.137) can be rearranged into dρ dU 1 dM 2 dx k M2 dP = =− =− 4f =− 2 P ρ U 2 M 2 (1 − k M 2 ) D

(13.138)

Similarly or by other paths, the stagnation pressure can be expressed as a function of 4f L D

  k+1 2 k M2 1 − M dx dP0 2   4f = k − 1 P0 D 2 (k M 2 − 1) 1 + M2 2 dT0 = T0

dx k (1 − k) M 2   4f k−1 2 D 2 (1 − k M 2 ) 1 + M 2

(13.139)

(13.140)

The variables in equation (13.138) can be separated to obtain integrable form as follows Z

0

L

4 f dx = D

Z

1/k

M2

1 − k M2 dM 2 k M2

(13.141)

It can be noticed that at the entrance (x = 0) for which M = Mx=0 (the initial velocity in the tube isn’t zero). The term 4fDL is positive for any x, thus, the term on the other side has to be positive as well. To obtain this restriction 1 = k M 2 . Thus, the value M = √1k is the limiting case from a mathematical point of view. When Mach number larger than M > √1k it makes the right hand side of the integrate negative. The physical meaning of this value is similar to M = 1 choked flow which was discussed in a variable area flow in Section 13.4. Further it can be noticed from equation (13.140) that when M → √1k the value of right hand side approaches infinity (∞). Since the stagnation temperature (T0 ) has

516

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

a finite value which means that dT0 → ∞. Heat transfer has a limited value therefore the model of the flow must be changed. A more appropriate model is an adiabatic flow model yet this model can serve as a bounding boundary (or limit). Integration of equation (13.141) requires information about the relationship between the length, x, and friction factor f . The friction is a function of the Reynolds number along the tube. Knowing the Reynolds number variations is important. The Reynolds number is defined as Re =

DU ρ µ

(13.142)

The quantity U ρ is constant along the tube (mass conservation) under constant area. Thus, only viscosity is varied along the tube. However under the assumption of ideal gas, viscosity is only a function of the temperature. The temperature in isothermal process (the definition) is constant and thus the viscosity is constant. In real gas, the pressure effects are very minimal as described in “Basic of fluid mechanics” by this author. Thus, the friction factor can be integrated to yield Friction Mach Isothermal Flow
4 f L 1 − k M2 = + ln k M 2 D k M2

(13.143)

max

The definition for perfect gas yields M 2 = U 2 /k R T and noticing that T = √ constant is used to describe the relation of the properties at M = 1/ k. By denoting the superscript symbol ∗ for the choking condition, one can obtain that M2 1/k = ∗2 2 U U Rearranging equation (13.144) is transformed into √ U = kM ∗ U Utilizing the continuity equation provides ρU = ρ∗ U ∗

=⇒

ρ 1 =√ ρ? kM

(13.144)

(13.145)

(13.146)

Reusing the perfect–gas relationship Pressure Ratio P ρ 1 = ∗ =√ P∗ ρ kM Utilizing the relation for stagnated isotropic pressure one can obtain " # k 2 k−1 M P0 P 1 + k−1 2 = ∗ P0∗ P 1 + k−1 2k

(13.147)

(13.148)

13.6. ISOTHERMAL FLOW

517

2

10

4f L D P/P∗ = ρ/ρ∗ P0 /P0 ∗ T0 /T0 ∗

10

1

10

-1

-2

10

0

1

2

3

4

5

6

7

8

9

10

M Fig. -13.18. Description of the pressure, temperature relationships as a function of the Mach number for isothermal flow.

Substituting for

P P∗

equation (13.147) and rearranging yields Stagnation Pressure Ratio

P0 1 =√ ∗ P0 k



2k 3k − 1



k k−1



k−1 2 1+ M 2



k k−1

1 M

(13.149)

And the stagnation temperature at the critical point can be expressed as Stagnation Pressure Ratio k−1 2   T 1+ 2 M 2k T0 k−1 = ∗ = 1+ M2 k−1 T0∗ T 3k − 1 2 1+ 2k

(13.150)

These equations (13.145)-(13.150) are presented on in Figure (13.18).

13.6.3

The Entrance Limitation of Supersonic Branch

This setion deals with situations where the conditions at the tube exit have not arrived at the critical condition. It is very useful to obtain the relationships between the entrance

518

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

and the exit conditions for this case. Denote 1 and 2 as the conditions at the inlet and exit respectably. From equation (13.138)  2 4f L 4 f L 1 − k M1 2 1 − k M2 2 M1 4 f L − = − + ln = D D max1 D max2 M2 k M1 2 k M2 2 (13.151) For the case that M1 >> M2 and M1 → 1 equation (13.151) is reduced into the following approximation ∼0

z }| { 1 − k M2 2 4f L = 2 ln (M1 ) − 1 − D kM2 2

(13.152)

Solving for M1 results in M1 ∼

e

1 2



 4f L +1 D

(13.153)

This relationship shows the maximum limit that Mach number can approach when the fL heat transfer is extraordinarily fast. In reality, even small 4 D > 2 results in a Mach number which is larger than 4.5. This velocity requires a large entrance length to achieve good heat transfer. With this conflicting mechanism obviously the flow is closer to the Fanno flow model. Yet this model provides the directions of the heat transfer effects on the flow. Example 13.14: 4f L = 3 under the assumption of the Calculate the exit Mach number for pipe with D isothermal flow and supersonic flow. Estimate the heat transfer needed to achieve this flow.

13.6.4

Supersonic Branch

Apparently, this analysis/model is over simplified for the supersonic branch and does not produce reasonable results since it neglects to take into account the heat transfer effects. A dimensionless analysis15 demonstrates that all the common materials that the author is familiar which creates a large error in the fundamental assumption of the model and the model breaks. Nevertheless, this model can provide a better understanding to the trends and deviations from Fanno flow model. In the supersonic flow, the hydraulic entry length is very large as will be shown below. However, the feeding diverging nozzle somewhat reduces the required entry length (as opposed to converging feeding). The thermal entry length is in the order 15 This dimensional analysis is a bit tricky, and is based on estimates. Currently and ashamedly the author is looking for a more simplified explanation. The current explanation is correct but based on hands waving and definitely does not satisfy the author.

13.6. ISOTHERMAL FLOW

519

of the hydrodynamic entry length (look at the Prandtl number16 , (0.7-1.0), value for the common gases.). Most of the heat transfer is hampered in the sublayer thus the core assumption of isothermal flow (not enough heat transfer so the temperature isn’t constant) breaks down17 . The flow speed at the entrance is very large, over hundred of meters per second. fL = 10 the required entry Mach number For example, a gas flows in a tube with 4 D is over 200. Almost all the perfect gas model substances dealt with in this book, the speed of sound is a function of temperature. For this illustration, for most gas cases the speed of sound is about 300[m/sec]. For example, even with low temperature like 200K the speed of sound of air is 283[m/sec]. So, even for relatively small tubes with 4f D D = 10 the inlet speed is over 56 [km/sec]. This requires that the entrance length to be larger than the actual length of the tub for air. Lentrance = 0.06

UD ν

(13.154)

The typical values of the the kinetic viscosity, ν, are 0.0000185 kg/m-sec at 300K and fL 0.0000130034 kg/m-sec at 200K. Combine this information with our case of 4 D = 10 Lentrance = 250746268.7 D On the other hand a typical value of friction coefficient f = 0.005 results in Lmax 10 = = 500 D 4 × 0.005 The fact that the actual tube length is only less than 1% of the entry length means that the assumption is that the isothermal flow also breaks (as in a large response time). If Mach number is changing from 10 to 1 the kinetic energy change is about TT00∗ = 18.37 which means that the maximum amount of energy is insufficient. Now with limitation, this topic will be covered in the next version because it provide some insight and boundary to the Fanno Flow model.

13.6.5

Figures and Tables

Table -13.4. The Isothermal Flow basic parameters P P∗

P0 P0 ∗

ρ ρ∗

0.03000 785.97

28.1718

17.6651

28.1718

0.87516

0.04000 439.33

21.1289

13.2553

21.1289

0.87528

M

16

4f L D

is relating thermal boundary layer to the momentum boundary layer. Kays and Crawford “Convective Heat Transfer” (equation 12-12).

17 See

T0 T0 ∗

520

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Table -13.4. The Isothermal Flow basic parameters (continue) P P∗

P0 P0 ∗

ρ ρ∗

0.05000 279.06

16.9031

10.6109

16.9031

0.87544

0.06000 192.12

14.0859

8.8493

14.0859

0.87563

0.07000 139.79

12.0736

7.5920

12.0736

0.87586

0.08000 105.89

10.5644

6.6500

10.5644

0.87612

M

4f L D

T0 T0 ∗

0.09000

82.7040

9.3906

5.9181

9.3906

0.87642

0.10000

66.1599

8.4515

5.3334

8.4515

0.87675

0.20000

13.9747

4.2258

2.7230

4.2258

0.88200

0.25000

7.9925

3.3806

2.2126

3.3806

0.88594

0.30000

4.8650

2.8172

1.8791

2.8172

0.89075

0.35000

3.0677

2.4147

1.6470

2.4147

0.89644

0.40000

1.9682

2.1129

1.4784

2.1129

0.90300

0.45000

1.2668

1.8781

1.3524

1.8781

0.91044

0.50000

0.80732

1.6903

1.2565

1.6903

0.91875

0.55000

0.50207

1.5366

1.1827

1.5366

0.92794

0.60000

0.29895

1.4086

1.1259

1.4086

0.93800

0.65000

0.16552

1.3002

1.0823

1.3002

0.94894

0.70000

0.08085

1.2074

1.0495

1.2074

0.96075

0.75000

0.03095

1.1269

1.0255

1.1269

0.97344

0.80000

0.00626

1.056

1.009

1.056

0.98700

0.81000

0.00371

1.043

1.007

1.043

0.98982

0.81879

0.00205

1.032

1.005

1.032

0.99232

0.82758

0.000896

1.021

1.003

1.021

0.99485

0.83637

0.000220

1.011

1.001

1.011

0.99741

0.84515

0.0

1.000

1.000

1.000

1.000

13.6. ISOTHERMAL FLOW

13.6.6

521

Isothermal Flow Examples

There can be several kinds of questions aside from the proof questions18 . Generally, the “engineering” or practical questions can be divided into driving force (pressure difference), resistance (diameter, friction factor, friction coefficient, etc.), and mass flow rate questions. In this model no questions about shock (should) exist19 . The driving force questions deal with what should be the pressure difference to obtain a certain flow rate. Here is an example. Example 13.15: A tube of 0.25 [m] diameter and 5000 [m] in length is attached to a pump. What should be the pump pressure so that a flow rate of 2 [kg/sec] will be achieved? Assume that friction factor f = 0.005 and the exit pressure is 1[bar]. i specific heat for the h The

gas, k = 1.31, surroundings temperature 27◦ C, R = 290 KJkg . Hint: calculate the maximum flow rate and then check if this request is reasonable. Solution

If the flow was incompressible then for known density, ρ, the velocity can be calculated f L U2 by utilizing ∆P = 4 D a function of the 2g . In incompressible flow, the density is √ entrance Mach number. The exit Mach number is not necessarily 1/ k i.e. the flow is not choked. First, check whether flow is choked (or even possible). fL Calculating the resistance, 4 D 4f L 4 × 0.0055000 = = 400 D 0.25 Utilizing Table (13.4) or the Potto–GDC provides M

4f l D

0.04331 400.00

P P∗

20.1743

P0 P0 ∗

12.5921

ρ ρ∗

0.0

T0 T0 ∗

0.89446

The maximum flow rate (the limiting case) can be calculated by utilizing the above table. The velocity of the gas at the entrance U = cM = 0.04331 × √ m 1.31 × 290 × 300 ∼ . The density reads = 14.62 sec ρ=

  P 2, 017, 450 ∼ kg = 23.19 = RT 290 × 300 m3

18 The proof questions are questions that ask for proof or for finding a mathematical identity (normally good for mathematicians and study of perturbation methods). These questions or examples will appear in the later versions. 19 Those who are mathematically inclined can include these kinds of questions but there are no real world applications to isothermal model with shock.

522

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

The maximum flow rate then reads

  π × (0.25)2 kg ∼ m ˙ = ρAU = 23.19 × × 14.62 = 16.9 4 sec

The maximum flow rate is larger then the requested mass rate hence the flow is not choked. It is note worthy to mention that since the isothermal model breaks around the choking point, the flow rate is really some what different. It is more appropriate to assume an isothermal model hence our model is appropriate. For incompressible flow, the pressure loss is expressed as follows P1 − P2 =

4 f L U2 D 2

(13.XV.a)

fL Now note that for incompressible flow U1 = U2 = U and 4 D represent the ratio of the traditional h12 . To obtain a similar expression for isothermal flow, a relationship between M2 and M1 and pressures has to be derived. From equation (13.XV.a) one can obtained that P1 (13.XV.b) M2 = M1 P2 To solve this problem the flow rate has to be calculated as   kg m ˙ = ρAU = 2.0 sec

m ˙ =

P1 kU P1 kU P1 A =√ A√ = Ak M1 RT k c kRT kRT

Now combining with equation (13.XV.b) yields m ˙ =

M2 =

M 2 P2 A k c

m ˙ c 2 × 337.59 = = 0.103 2 P2 A k 100000 × π×(0.25) × 1.31 4

From Table (13.4) or by utilizing the Potto–GDC one can obtain M 0.10300

4f L D

66.6779

P P∗

P0 P0 ∗

8.4826

5.3249

ρ ρ∗

0.0

The entrance Mach number is obtained by 4 f L = 66.6779 + 400 ∼ = 466.68 D 1 Hence,

T0 T0 ∗

0.89567

13.6. ISOTHERMAL FLOW 4f L D

M

523 P0 P0 ∗

P P∗

0.04014 466.68

21.7678

13.5844

ρ ρ∗

0.0

T0 T0 ∗

0.89442

The pressure should be P = 21.76780 × 8.4826 = 2.566[Bar] Note that tables in this example are for k = 1.31 End Solution

Example 13.16: A flow of gas was considered for a distance of 0.5 [km] (500 [m]). A flow rate of 0.2 [kg/sec] is required. Due to safety concerns, the maximum pressure allowed for the gas is only 10[bar]. Assume that the flow is isothermal and k=1.4, calculate the required diameter of tube. The friction coefficient for the tube can be assumed as 0.02 (A relative smooth tube of cast iron.). Note that tubes are provided in increments of 0.5 [in]20 . You can assume that the soundings temperature to be 27◦ C. Solution At first, the minimum diameter will be obtained when the flow is choked. Thus, the maximum M1 that can be obtained when the M2 is at its maximum and back pressure is at the atmospheric pressure. Mmax

z}|{ P2 1 1 M1 = M2 = 0.0845 = √ P1 k 10 Now, with the value of M1 either by utilizing Table 13.4 or using the provided program yields 4f L D

M 0.08450 4 f L With D D=

20 It

P P∗

94.4310

10.0018

P0 P0 ∗

6.2991

ρ ρ∗

0.0

T0 T0 ∗

0.87625

= 94.431, the value of minimum diameter. max

4f L

4f L D max

'

4 × 0.02 × 500 ' 0.42359[m] = 16.68[in] 94.43

is unfortunate, but it seems that this standard will be around in USA for some time.

524

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

However, the pipes are provided only in 0.5 increments and the next size is 17[in] or 0.4318[m]. With this pipe size the calculations are to be repeated in reverse and produces: (Clearly the maximum mass is determined with) √ √ P P AM k m ˙ = ρAU = ρAM c = AM kRT = √ RT RT The usage of the above equation clearly applied to the whole pipe. The only point that must be emphasized is that all properties (like Mach number, pressure and etc) have 4f L to be taken at the same point. The new is D 4 × 0.02 × 500 4f L = ' 92.64 D 0.4318 M 0.08527

4f L D

92.6400

P P∗

P0 P0 ∗

9.9110

6.2424

ρ ρ∗

1.0

T0 T0 ∗

0.87627

To check whether the flow rate satisfies the requirement √ 2 106 × π×0.4318 × 0.0853 × 1.4 4 √ m ˙ = ≈ 50.3[kg/sec] 287 × 300 Since 50.3 ≥ 0.2 the mass flow rate requirement is satisfied. It should be noted that P should be replaced by P0 in the calculations. The speed of sound at the entrance is hmi √ √ c = k R T = 1.4 × 287 × 300 ∼ = 347.2 sec

and the density is

ρ=

  P 1, 000, 000 kg = = 11.61 RT 287 × 300 m3

The velocity at the entrance should be U = M ∗ c = 0.08528 × 347.2 ∼ = 29.6 The diameter should be D=

s

4m ˙ = πU ρ

r

hmi sec

4 × 0.2 ∼ = 0.027 π × 29.6 × 11.61

Nevertheless, for the sake of the exercise the other parameters will be calculated. This situation is reversed question. The flow rate is given with the diameter of the pipe. It should be noted that the flow isn’t choked. End Solution

13.6. ISOTHERMAL FLOW

525

Example 13.17: A gas flows of from a station (a) with pressure of 20[bar] through a pipe with 0.4[m] diameter and 4000 [m] length to a different station (b). The pressure at the exit (station (b)) is 2[bar]. The gas and the sounding temperature can be assumed to be 300 K. Assume that the flow is isothermal, k=1.4, and the average friction f=0.01. Calculate the Mach number at the entrance to pipe and the flow rate. Solution First, the information whether the flow is choked needs to be found. Therefore, at first it will be assumed that the whole length is the maximum length.

with



4f L D

4 × 0.01 × 4000 4 f L = = 400 D max 0.4

max

M

0.0419

= 400 the following can be written

400.72021

ρ ρ∗T

T0 T0 ∗T

4f L D

0.87531

20.19235

From the table M1 ≈ 0.0419 ,and P0 ∗T ∼ =

P P∗T

P0 P0 ∗T

20.19235

P0 P0 ∗T

12.66915

≈ 12.67

28 ' 2.21[bar] 12.67

The pressure at point (b) by utilizing the isentropic relationship (M = 1) pressure ratio is 0.52828. P2 = 

P0 ∗T  = 2.21 × 0.52828 = 1.17[bar] P2 P0 ∗T

As the pressure at point (b) is smaller than the actual pressure P ? < P2 than the actual pressure one must conclude that the flow is not choked. The solution is an iterative process. fL 1. Guess reasonable value of M1 and calculate 4 D f L f L 2. Calculate the value of 4 D by subtracting 4 D − 2

1

4f L D

3. Obtain M2 from the Table ? or by using the Potto–GDC.

4.

Calculate the pressure, P2 bear in mind that this isn’t the real pressure but based on the assumption.

526 5.

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Compare the results of guessed pressure P2 with the actual pressure and choose new Mach number M1 accordingly.

The process has been done and is provided in Figure or in a table obtained from Potto– GDC. P2 4f L 4f L M1 M2 D max 1 D P1 0.0419

0.59338

400.32131

400.00000

0.10000

The flow rate is √ √ P k π × D2 2000000 1.4 m ˙ = ρAM c = √ π × 0.22 × 0.0419 M= √ 4 300 × 287 RT ' 42.46[kg/sec] End Solution

In this chapter, there are no examples on isothermal with supersonic flow.

Table -13.5. The flow parameters for unchoked flow

13.7



0.7272

0.84095

0.6934

0.83997

0.08978

0.08971

0.10000

0.6684

0.84018

0.12949

0.12942

0.10000

0.6483

0.83920

0.16922

0.16912

0.10000

0.5914

0.83889

0.32807

0.32795

0.10000

0.5807

0.83827

0.36780

0.36766

0.10000

0.5708

0.83740

0.40754

0.40737

0.10000

M2

0.05005

the friction does not convert into heat

P2 P1

4f L D

0.05000

0.10000

Fanno Flow

This adiabatic flow model with friction is named after Ginno Fanno a Jewish engineer. This model is the second pipe flow model described here. The main restriction for this model is that heat transfer is negligible and can be ignored 21 . This model is applicable to flow processes which 21 Even



4f L D max 1

M1

w

flow direction

T U

o

ρ P

ρ + ∆ρ P + ∆P T + ∆T U + ∆U

(M) w

(M + ∆M)

c.v.

No heat transer

Fig. -13.19. Control volume of the gas flow in a constant cross section for Fanno Flow.

13.7.

FANNO FLOW

527

are very fast compared to heat transfer mechanisms with small Eckert number. This model explains many industrial flow processes which includes emptying of pressured container through a relatively short tube, exhaust system of an internal combustion engine, compressed air systems, etc. As this model raised from the need to explain the steam flow in turbines.

13.7.1

Introduction

Consider a gas flowing through a conduit with a friction (see Figure 13.19). It is advantages to examine the simplest situation and yet without losing the core properties of the process. The mass (continuity equation) balance can be written as m ˙ = ρ A U = constant

(13.155)

,→ ρ1 U1 = ρ2 U2 The energy conservation (under the assumption that this model is adiabatic flow and the friction is not transformed into thermal energy) reads T01 U1 2 ,→ T1 + 2 cp

= T02 = T2 +

U2 2 2 cp

(13.156)

Or in a derivative from Cp dT + d



U2 2



=0

(13.157)

Again for simplicity, the perfect gas model is assumed22 . P = ρRT ,→

P1 P2 = ρ1 T1 ρ2 T2

(13.158)

It is assumed that the flow can be approximated as one–dimensional. The force acting on the gas is the friction at the wall and the momentum conservation reads −A dP − τw dAw = m ˙ dU

(13.159)

It is convenient to define a hydraulic diameter as DH = 22 The

4 × Cross Section Area wetted perimeter

(13.160)

equation of state is written again here so that all the relevant equations can be found.

528

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Or in other words A=

π DH 2 4

(13.161)

It is convenient to substitute D for DH and yet it still will be referred to the same name as the hydraulic diameter. The infinitesimal area that shear stress is acting on is dAw = π D dx

(13.162)

Introducing the Fanning friction factor as a dimensionless friction factor which is some times referred to as the friction coefficient and reads as the following: f=

1 2

τw ρ U2

(13.163)

By utilizing equation (13.155) and substituting equation (13.163) into momentum equation (13.159) yields A

τ

w m ˙ z }| { z  }| A { 2 z}|{ 1 πD − dP − π D dx f ρ U 2 = A ρ U dU 4 2

(13.164)

Dividing equation (13.164) by the cross section area, A and rearranging yields −dP +

4 f dx D



1 ρ U2 2



= ρ U dU

(13.165)

The second law is the last equation to be utilized to determine the flow direction. s2 ≥ s1

13.7.2

(13.166)

Non–Dimensionalization of the Equations

Before solving the above equation a dimensionless process is applied. By utilizing the definition of the sound speed to produce the following identities for perfect gas 2

M =



U c

2

=

U2 k |{z} RT

(13.167)

P ρ

Utilizing the definition of the perfect gas results in M2 =

ρ U2 kP

(13.168)

13.7.

FANNO FLOW

529

Using the identity in equation (13.167) and substituting it into equation (13.164) and after some rearrangement yields

−dP +

4 f dx DH



1 k P M2 2



ρU 2

z }| { dU ρU dU = k P M 2 = U U 2

By further rearranging equation (13.169) results in   dP 4 f dx k M 2 dU − − = k M2 P D 2 U

(13.169)

(13.170)

It is convenient to relate expressions of dP/P and dU/U in terms of the Mach number and substituting it into equation (13.170). Derivative of mass conservation (13.155) results in dU U z }| { dρ 1 dU 2 + =0 ρ 2 U2

(13.171)

The derivation of the equation of state (13.158) and dividing the results by equation of state (13.158) results dρ dT dP = + P ρ dT

(13.172)

Differentiating of equation (13.167) and dividing by equation (13.167) yields d(M 2 ) d(U 2 ) dT = − 2 M U2 T

(13.173)

Dividing the energy equation (13.157) by Cp and by utilizing the definition Mach number yields  2 dT 1 U 1 U2  + d = 2 k R T TU 2 (k − 1) | {z } Cp

,→

(k − 1) U 2 dT + d 2 T k |R {zT} U c2



U2 2



(13.174)

=

dT k − 1 2 dU 2 ,→ + M =0 T 2 U2 Equations (13.170), (13.171), (13.172), (13.173), and (13.174) need to be solved. These equations are separable so one variable is a function of only single variable (the

530

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

chosen as the independent variable). Explicit explanation is provided for only two variables, the rest variables can be done in a similar fashion. The dimensionless friction, 4f L D , is chosen as the independent variable since the change in the dimensionless resisfL tance, 4 D , causes the change in the other variables. Combining equations (13.172) and (13.174) when eliminating dT /T results dρ (k − 1) M 2 dU 2 dP = − P ρ 2 U2

(13.175)

The term dρ/ ρ can be eliminated by utilizing equation (13.171) and substituting it into equation (13.175) and rearrangement yields dP 1 + (k − 1) M 2 dU 2 =− P 2 U2 The term dU 2 /U 2 can be eliminated by using (13.176)
k M 2 1 + (k − 1) M 2 4 f dx dP =− P 2 (1 − M 2 ) D

(13.176)

(13.177)

The second equation for Mach number, M variable is obtained by combining equation (13.173) and (13.174) by eliminating dT /T . Then dρ/ρ and U are eliminated by utilizing equation (13.171) and equation (13.175). The only variable that is left is P (or dP/P ) which can be eliminated by utilizing equation (13.177) and results in
1 − M 2 dM 2 4 f dx = (13.178) k−1 2 D k M 4 (1 + M ) 2 Rearranging equation (13.178) results in   k−1 2 2 k M 1 + M dM 2 4 f dx 2 = M2 1 − M2 D

(13.179)

After similar mathematical manipulation one can get the relationship for the velocity to read dU k M2 4 f dx = 2 U 2 (1 − M ) D

(13.180)

and the relationship for the temperature is dT 1 dc k (k − 1) M 4 4 f dx = =− T 2 c 2 (1 − M 2 ) D

(13.181)

density is obtained by utilizing equations (13.180) and (13.171) to obtain dρ k M2 4 f dx =− ρ 2 (1 − M 2 ) D

(13.182)

13.7.

FANNO FLOW

531

The stagnation pressure is similarly obtained as dP0 k M 2 4 f dx =− P0 2 D

(13.183)

The second law reads ds = Cp ln



dT T



− R ln



dP P



(13.184)

The stagnation temperature expresses as T0 = T (1 + (1 − k)/2M 2 ). Taking derivative of this expression when M remains constant yields dT0 = dT (1 + (1 − k)/2M 2 ) and thus when these equations are divided they yield dT /T = dT0 /T0

(13.185)

In similar fashion the relationship between the stagnation pressure and the pressure can be substituted into the entropy equation and result in     dP0 dT0 − R ln (13.186) ds = Cp ln T0 P0 The first law requires that the stagnation temperature remains constant, (dT0 = 0). Therefore the entropy change is (k − 1) dP0 ds =− Cp k P0

(13.187)

Using the equation for stagnation pressure the entropy equation yields ds (k − 1) M 2 4 f dx = Cp 2 D

13.7.3

(13.188)

The Mechanics and Why the Flow is Choked?

The trends of the properties can be examined by looking in equations (13.177) through (13.187). For example, from equation (13.177) it can be observed that the critical point is when M = 1. When M < 1 the pressure decreases downstream as can be seen from equation (13.177) because f dx and M are positive. For the same reasons, in the supersonic branch, M > 1, the pressure increases downstream. This pressure increase is what makes compressible flow so different from “conventional” flow. Thus the discussion will be divided into two cases: One, flow above speed of sound. Two, flow with speed below the speed of sound. 13.7.3.1

Why the flow is choked?

Here, the explanation is based on the equations developed earlier and there is no known explanation that is based on the physics. First, it has to be recognized that the critical

532

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

point is when M = 1. It will be shown that a change in location relative to this point change the trend and it is singular point by itself. For example, dP (@M = 1) = ∞ and mathematically it is a singular point (see equation (13.177)). Observing from equation (13.177) that increase or decrease from subsonic just below one M = (1 − ) to above just above one M = (1 + ) requires a change in a sign pressure direction. However, the pressure has to be a monotonic function which means that flow cannot crosses over the point of M = 1. This constrain means that because the flow cannot “crossover” M = 1 the gas has to reach to this speed, M = 1 at the last point. This situation is called choked flow. 13.7.3.2

The Trends

The trends or whether the variables are increasing or decreasing can be observed from looking at the equation developed. For example, the pressure can be examined by looking at equation (13.179). It demonstrates that the Mach number increases downstream when the flow is subsonic. On the other hand, when the flow is supersonic, the pressure decreases. The summary of the properties changes on the sides of the branch

13.7.4

Subsonic

Supersonic

Pressure, P

decrease

increase

Mach number, M

increase

decrease

Velocity, U

increase

decrease

Temperature, T

decrease

increase

Density, ρ

decrease

increase

The Working Equations

Integration of equation (13.178) yields

4 D

Z

Fanno FLD–M Lmax

L

f dx =

k+1 2 1 1 − M2 k+1 2 M + ln k−1 k M2 2k 1 + 2 M2

(13.189)

A representative friction factor is defined as f¯ =

1 Lmax

Z

Lmax

f dx

(13.190)

0

In the isothermal flow model it was shown that friction factor is constant through the process if the fluid is ideal gas. Here, the Reynolds number defined in equation (13.142)

13.7.

FANNO FLOW

533

is not constant because the temperature is not constant. The viscosity even for ideal gas is complex function of the temperature (further reading in “Basic of Fluid Mechanics” chapter one, Potto Project). However, the temperature variation is very limited. Simple improvement can be done by assuming constant constant viscosity (constant friction factor) and find the temperature on the two sides of the tube to improve the friction factor for the next iteration. The maximum error can be estimated by looking at the maximum change of the temperature. The temperature can be reduced by less than 20% for most range of the specific heats ratio. The viscosity change for this change is for many gases about 10%. For these gases the maximum increase of average Reynolds number is only 5%. What this change in Reynolds number does to friction factor? That depend in the range of Reynolds number. For Reynolds number larger than 10,000 the change in friction factor can be considered negligible. For the other extreme, laminar flow it can estimated that change of 5% in Reynolds number change about the same amount in friction factor. With the exception of the jump from a laminar flow to a turbulent flow, the change is noticeable but very small. In the light of the about discussion the friction factor is assumed to constant. By utilizing the mean average theorem equation (13.189) yields

4 f Lmax D

Resistance Mach Relationship   k+1 2   M 2 1 1−M k+1   2 = ln  + k − 1 2 k M2 2k 1+ M 2

(13.191)

Equations (13.177), (13.180), (13.181), (13.182), (13.182), and (13.183) can be solved. For example, the pressure as written in equation (13.176) is represented by 4fDL , and Mach number. Now equation (13.177) can eliminate term 4fDL and describe the pressure on the Mach number. Dividing equation (13.177) in equation (13.179) yields dP 1 + (k − 1M 2 P =−  dM 2  k−1 2 dM 2 2 M 2M 1 + 2 M2

(13.192)

The symbol “?” denotes the state when the flow is choked and Mach number is equal to 1. Thus, M = 1 when P = P ∗ equation (13.192) can be integrated to yield: Mach–Pressure Ratio v u k+1 u P 1 u 2 u = k−1 2 P∗ Mt 1+ M 2

(13.193)

534

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

In the same fashion the variables ratios can be obtained Temperature Ratio k+1 2 k−1 2 1+ M 2

(13.194)

Density Ratio v u u1 + k − 1M2 ρ 1 u 2 u = k+1 ρ∗ Mt 2

(13.195)

Velocity Ratio v u k+1 u  −1 u ρ U 2 = = Mu t k−1 2 U∗ ρ∗ 1+ M 2

(13.196)

c2 T = ∗2 = ∗ T c

The density ratio is

The velocity ratio is

The stagnation pressure decreases and can be expressed by 

1−k 1+ 2 M 2

P0 = P0 ? 

z}|{ P0 P P0 ∗ P∗ |{z}

2 k+1

 k k−1

P (13.197) P∗

 k k−1

Using the pressure ratio in equation (13.193) and substituting it into equation (13.197) yields

P0 P0 ∗

v  k u k − 1 2 k−1 u1 + k − 1 M2 1+ M u 1   2 2 u =  k+1 k+1 Mt 2 2 

(13.198)

13.7.

FANNO FLOW

535

2

10

4f L D P/P∗ P0 /P0 ∗ ρ/ρ∗ U/U∗ T/T∗

10

1

10

-1

-2

10

0

1

2

3

4

5

6

7

8

9

10

M Fig. -13.20. Various parameters in Fanno flow shown as a function of Mach number.

And further rearranging equation (13.198) provides

Stagnation Pressure Ratio P0 P0 ∗

 k+1 k − 1 2 2 (k−1) 1 1 + 2 M  =   k+1 M 2 

(13.199)

The integration of equation (13.187) yields v u u u u ∗ s−s u = ln M 2 u t Cp

 k+1 k

2 M2



k+1 k−1 2 1+ M 2

  

(13.200)

The results of these equations are plotted in Figure 13.20 The Fanno flow is in many cases shockless and therefore a relationship between two points should be derived. In most times, the “star” values are imaginary values that represent the value at choking. The real ratio can be obtained by two star ratios

536

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

as an example T T ∗ M2 T2 = T T1 T∗

(13.201)

M1

A special interest is the equation for the dimensionless friction as following Z

L2

L1

4f L dx = D

Z

Lmax

L1

4f L dx − D

Z

Lmax

L2

4f L dx D

(13.202)

Hence, 

13.7.5

fld Working Equation    4 f Lmax 4f L 4 f Lmax = − D D D 2 1

(13.203)

Examples of Fanno Flow

Example 13.18: Air flows from a reservoir and enters a uniform pipe with a diameter of 0.05 [m] and length of 10 [m]. The air exits to the atmosphere. M2 = 0.9 D = 0.05[m] The following conditions prevail at L = 10[m] P0 =? the exit: P2 = 1[bar] temperature ◦C ◦ 23 T =? 0 T2 = 27◦C T2 = 27 C M2 = 0.9 . Assume P2 = 1[Bar] that the average friction factor to be f = 0.004 and that the flow from the reservoir up to the pipe Fig. -13.21. Schematic of Example 13.18. inlet is essentially isentropic. Estimate the total temperature and total pressure in the reservoir under the Fanno flow model. Solution For isentropic, the flow to the pipe inlet, the temperature and the total pressure at the pipe inlet are the same as those in the reservoir. Thus, finding the star pressure and temperature at the pipe inlet is the solution. With the Mach number and temperature known at the exit, the total temperature at the entrance can be obtained by knowing the 4fDL . For given Mach number (M = 0.9) the following is obtained. M

4f L D

P P∗

0.90000 0.01451 1.1291 23 This

P0 P0 ∗

ρ ρ∗

U U∗

T T∗

1.0089

1.0934

0.9146

1.0327

property is given only for academic purposes. There is no Mach meter.

13.7.

FANNO FLOW

537

So, the total temperature at the exit is 300 T ∗ ∗ T2 = T |2 = = 290.5[K] T 2 1.0327 To “move” to the other side of the tube the

4f L D

1

=

4f L D

+



4f L D 2

=

4f L D

is added as

4 × 0.004 × 10 + 0.01451 ' 3.21 0.05

The rest of the parameters can be obtained with the new by interpolations or by utilizing the attached program. 4f L D

M

0.35886 3.2100

P P∗

P0 P0 ∗

ρ ρ∗

3.0140

1.7405

2.5764

4f L D

either from Table 13.6

U U∗

T T∗

0.38814 1.1699

Note that the subsonic branch is chosen. The stagnation ratios has to be added for M = 0.35886 ρ ρ0

T T0

M

A A?

0.35886 0.97489 0.93840 1.7405

P P0

A×P A∗ ×P0

0.91484 1.5922

F F∗

0.78305

The total pressure P01 can be found from the combination of the ratios as follows: P

P01

z }|1 { P∗ z }| { P ∗ P P0 = P2 P 2 P ∗ 1 P 1 1 1 =1 × × 3.014 × = 2.91[Bar] 1.12913 0.915

T

T01

z }|1 { ∗ T z }| { T ∗ T T0 = T2 T 2 T ∗ 1 T 1 1 1 =300 × × 1.17 × ' 348K = 75◦ C 1.0327 0.975 End Solution

Another academic question/example:

538

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Example 13.19: Mx =? A system is composed of a convergentD = 0.025[m] divergent nozzle followed by a tube with M1 = 3.0 L = 1.0[m] P0 = 29.65[Bar] length of 2.5 [cm] in diameter and 1.0 [m] shock T0 = 400K long. The system is supplied by a vessel. atmospheric d-c nozzle conditions The vessel conditions are at 29.65 [Bar], 400 K. With these conditions a pipe inlet Mach number is 3.0. A normal shock wave occurs Fig. -13.22. The schematic of Example in the tube and the flow discharges to the (13.19). atmosphere, determine:

(a) the mass flow rate through the system; (b) the temperature at the pipe exit; and (c) determine the Mach number when a normal shock wave occurs [Mx ]. Take k = 1.4, R = 287 [J/kgK] and f = 0.005. Solution

(a) Assuming that the pressure vessel is very much larger than the pipe, therefore the velocity in the vessel can be assumed to be small enough so it can be neglected. Thus, the stagnation conditions can be approximated for the condition in the tank. It is further assumed that the flow through the nozzle can be approximated as isentropic. Hence, T01 = 400K and P01 = 29.65[P ar]. The mass flow rate through the system is constant and for simplicity point 1 is chosen in which, m ˙ = ρAM c The density and speed of sound are unknowns and need to be computed. With the isentropic relationship, the Mach number at point one (1) is known, then the following can be found either from Table 13.6, or the popular Potto–GDC as

M 3.0000

T T0

ρ ρ0

A A?

0.35714 0.07623 4.2346

P P0

A×P A∗ ×P0

F F∗

0.02722 0.11528 0.65326

13.7.

FANNO FLOW

539

The temperature is T1 =

T1 T01 = 0.357 × 400 = 142.8K T01

Using the temperature, the speed of sound can be calculated as √ √ c1 = k R T = 1.4 × 287 × 142.8 ' 239.54[m/sec] The pressure at point 1 can be calculated as P1 =

P1 P01 = 0.027 × 30 ' 0.81[Bar] P01

The density as a function of other properties at point 1 is   8.1 × 104 kg P = ' 1.97 ρ1 = R T 1 287 × 142.8 m3

The mass flow rate can be evaluated from equation (13.155)   kg π × 0.0252 × 3 × 239.54 = 0.69 m ˙ = 1.97 × 4 sec (b) First, check whether the flow is shockless by comparing the flow resistance and the maximum possible resistance. From the Table 13.6 or by using the famous Potto–GDC, is to obtain the following M 3.0000

4f L D

P0 P0 ∗

P P∗

0.52216 0.21822 4.2346

ρ ρ∗

U U∗

0.50918 1.9640

T T∗

0.42857

and the conditions of the tube are 4f L D

=

4 × 0.005 × 1.0 = 0.8 0.025

Since 0.8 > 0.52216 the flow is choked and with a shock wave. The exit pressure determines the location of the shock, if a shock exists, by comparing “possible” Pexit to PB . Two possibilities are needed to be checked; one, the shock at the entrance of the tube, and two, shock at the exit and comparing the pressure ratios. First, the possibility that the shock wave occurs immediately at the entrance for which the ratio for Mx are (shock wave Table 13.3)

540

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

Mx

My

Ty Tx

ρy ρx

3.0000

0.47519

2.6790

3.8571

P0 y P0 x

Py Px

10.3333

0.32834

After the shock wave the flow is subsonic with “M1 ”= 0.47519. (Fanno Flow Table 13.6) 4f L D

M

0.47519 1.2919

P P∗

P0 P0 ∗

ρ ρ∗

2.2549

1.3904

1.9640

U U∗

T T∗

0.50917 1.1481

The stagnation values for M = 0.47519 are T T0

M

ρ ρ0

A A?

0.47519 0.95679 0.89545 1.3904

P P0

A×P A∗ ×P0

F F∗

0.85676 1.1912

0.65326

The ratio of exit pressure to the chamber total pressure is 1

P2 = P0 = =

1

z }| { z }| {      P0y P∗ P2 P1 P0x ∗ P P1 P0y P0x P0 1 1× × 0.8568 × 0.32834 × 1 2.2549 0.12476

The actual pressure ratio 1/29.65 = 0.0338 is smaller than the case in which shock occurs at the entrance. Thus, the shock is somewhere downstream. One possible way to find the exit temperature, T2 is by finding the location of the 2 shock. To find the location of the shock ratio of the pressure ratio, P P1 is needed. With the location of shock, “claiming” upstream from the exit through shock to the entrance. For example, calculate the parameters for shock location with known 4fDL in the “y” side. Then either by utilizing shock table or the program, to obtain the upstream Mach number. The procedure for the calculations: Calculate the entrance Mach number assuming the shock occurs at the exit: 0

1) a) set M2 = 1 assume the flow in the entire tube is supersonic: 0 b) calculated M1 Note this Mach number is the high Value.

13.7.

FANNO FLOW

541

Calculate the entrance Mach assuming shock at the entrance. a) Set M2 = 1 2) b) Add 4fDL and calculated M1 ’ for subsonic branch c) Calculated Mx for M1 ’ Note this Mach number is the low value. According your root finding algorithm24 calculate or guess the shock location and then compute as above the new M1 . a) set M2 = 1 3) b) for the new 4f L and compute the new M ’ for the subsonic branch y D c) calculated Mx ’ for the My ’ d) Add the leftover of

4f L D

and calculated the M1

4) guess new location for the shock according to your finding root procedure and according to the result, repeat previous stage until the solution is obtained.

M1

M2

3.0000

1.0000



4f L D up

0.22019



4f L D down

0.57981

Mx

My

1.9899

0.57910

(c) The way of the numerical procedure for solving this problem is by finding



4f L D

up

that will produce M1 = 3. In the process Mx and My must be calculated (see the chapter on the program with its algorithms.). End Solution

Supersonic Branch In Section (13.6) it was shown that the isothermal model cannot describe adequately the situation because the thermal entry length is relatively large compared to the pipe length and the heat transfer is not sufficient to maintain constant temperature. In the Fanno model there is no heat transfer, and, furthermore, because the very limited amount of heat transformed it is closer to an adiabatic flow. The only limitation of the model is its uniform velocity (assuming parabolic flow for laminar and different profile for turbulent flow.). The information from the wall to the tube center25 is slower in reality. However, experiments from many starting with 1938 work by Frossel26 has shown that the error is not significant. Nevertheless, the comparison with reality shows that heat transfer cause changes to the flow and they need/should to be expected. These changes include the choking point at lower Mach number. 24 You

can use any method you wish, but be-careful second order methods like Newton-Rapson method can be unstable. 25 The word information referred to is the shear stress transformed from the wall to the center of the tube. 26 See on the web http://naca.larc.nasa.gov/digidoc/report/tm/44/NACA-TM-844.PDF

542 13.7.5.1

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL Maximum Length for the Supersonic Flow

It has to be noted and recognized that as opposed to subsonic branch the supersonic branch has a limited length. It also must be recognized that there is a maximum length for which only supersonic flow can exist27 . These results were obtained from the mathematical derivations but were verified by numerous experiments28 . The maximum length of the supersonic can be evaluated when M = ∞ as follows: k+1 2 k+1 4 f Lmax 1 − M2 2 M
= + = ln k−1 2 D kM 2k 2 1 + 2 M2 4f L D

−∞ k + 1 (k + 1) ∞ + ln = k×∞ 2k (k − 1) ∞ (k + 1) −1 k + 1 + ln = 4fDL (M → ∞, k = 1.4) = 0.8215 k 2k (k − 1)

(M → ∞) ∼

4 f Lmax = D

4f L D (M

→ ∞, k = 1.4) = 0.8215

(13.204)

The maximum length of the supersonic flow is limited by the above number. From the above analysis, it can be observed that no matter how high the entrance Mach number will be the tube length is limited and depends only on specific heat ratio, k.

13.7.6

Working Conditions 







4 f L1 4 f L2 It has to be recognized that there are two regimes < ∆s ∆s D D that can occur in Fanno flow model one of subsonic T 4f L flow and the other supersonic flow. Even the flow Larger =⇒ D T0 in the tube starts as a supersonic in parts of the tube can be transformed into the subsonic branch. A shock wave can occur and some portions of the tube will be in a subsonic flow pattern. s The discussion has to differentiate between two ways of feeding the tube: converging nozzle or a converging-diverging nozzle. Three parame- Fig. -13.23. The effects of increase of fL fL on the Fanno line. ters, the dimensionless friction, 4 D , the entrance 4 D Mach number, M1 , and the pressure ratio, P2 /P1 are controlling the flow. Only a combination of these two parameters is truly independent. However, all the three parameters can be varied and some are discussed separately here. 27 Many in the industry have difficulties in understanding this concept. The author seeks for a nice explanation of this concept for non–fluid mechanics engineers. This solicitation is about how to explain this issue to non-engineers or engineer without a proper background. 28 If you have experiments demonstrating this point, please provide to the undersign so they can be added to this book. Many of the pictures in the literature carry copyright statements and thus can be presented here.

13.7.

FANNO FLOW

13.7.6.1

543

Variations of The Tube Length ( 4fDL ) Effects

In the analysis of this effect, it should be assumed that back pressure is constant and/or low as possible as needed to maintain a choked flow. First, the treatment of the two branches are separated. Fanno Flow Subsonic branch constant pressure lines For converging nozzle feeding, increasT ing the tube length results in increasing the T0 1’’ exit Mach number (normally denoted herein as 2’’ 1’ M2 ). Once the Mach number reaches maxi1 2’ mum (M = 1), no further increase of the exit 2 Mach number can be achieved with same presFanno lines s sure ratio mass flow rate. For increase in the pipe length results in mass flow rate decreases. -13.24. The effects of the increase of It is worth noting that entrance Mach number Fig. 4f L on the Fanno Line. D is reduced (as some might explain it to reduce the flow rate). The entrance temperature increases as can be seen from Figure 13.24. The velocity therefore must decrease because the loss of the enthalpy (stagnation temperature) is “used.” The density decrease because ρ = RPT and when pressure is remains almost constant the density decreases. Thus, the mass flow rate must decrease. These results are applicable to the converging nozzle. In the case of the converging–diverging feeding nozzle, increase of the dimensionless friction, 4fDL , results in a similar flow pattern as in the converging nozzle. Once the flow becomes choked a different flow pattern emerges.

13.7.6.2

Fanno Flow Supersonic Branch

There are several transitional points that change the pattern of the flow. Point a M1 is the choking point (for the supersonic a M branch) in which the exit Mach number m ˙ M2 b c reaches to one. Point b is the maximum M=1 all supersonic possible flow for supersonic flow and is not flow dependent on the nozzle. The next point, m ˙ = const mixed supersonic with subsonic referred here as the critical point c, is the flow with a shock the nozzle between is still point in which no supersonic flow is poschoked sible in the tube i.e. the shock reaches 4 f L M1 D to the nozzle. There is another point d, in which no supersonic flow is possible in the entire nozzle–tube system. Between Fig. -13.25. The Mach numbers at entrance rate for Fanno these transitional points the effect param- and exit of tube and mass4fflow Flow as a function of the DL . eters such as mass flow rate, entrance and exit Mach number are discussed.

544

CHAPTER 13. COMPRESSIBLE FLOW ONE DIMENSIONAL

At the starting point the flow is choked in the nozzle, to achieve supersonic flow. The following ranges that has to be discussed includes (see Figure 13.25):

0 





4f L D

4f L D

4f L D





choking

shockless chokeless

4f L D


µ1 ). If the situation be generated at zero inclination. keeps on occurring over a finite distance, there will be a point where the Mach number will be 1 and a normal shock will occur, according the common explanation. However, the reality is that no continuous Mach wave can occur because of the viscosity (boundary layer). In reality, there are imperfections in the wall and in the flow and there is the question of boundary layer. It is well known, in the engineering world, that there is no such thing as a perfect wall. The imperfections of the wall can be, for simplicity’s sake, assumed to be as a sinusoidal shape. For such a wall the zero inclination changes from small positive value to a negative value. If the Mach number is large enough and the wall is rough enough, there will be points where a weak14 weak will be created. On the other hand, the boundary layer covers or smooths out the bumps. With these conflicting mechanisms, both will not allow a situation of zero inclination with emission of Mach wave. At the very extreme case, only in several points (depending on the bumps) at the leading edge can a very weak shock occur. Therefore, for the purpose of an introductory class, no Mach wave at zero inclination should be assumed. Furthermore, if it was assumed that no boundary layer exists and the wall is perfect, any deviations from the zero inclination angle creates a jump from a positive angle (Mach wave) to a negative angle (expansion wave). This theoretical jump occurs because in a Mach wave the velocity decreases while in the expansion wave the velocity increases. Furthermore, the increase and the decrease depend on the upstream Mach number but in different directions. This jump has to be in reality either smoothed out or has a physical meaning of jump (for example, detach normal shock). The analysis started by looking at a normal shock which occurs when there is a zero inclination. After analysis of the oblique shock, the same conclusion must be reached, i.e. that the 13 A

mathematical challenge for those who like to work it out. is not a mistake, there are two “weaks.” These words mean two different things. The first “weak” means more of compression “line” while the other means the weak shock. 14 It

596

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

normal shock can occur at zero inclination. The analysis of the oblique shock suggests that the inclination angle is not the source (boundary condition) that creates the shock. There must be another boundary condition(s) that causes the normal shock. In the light of this discussion, at least for a simple engineering analysis, the zone in the proximity of zero inclination (small positive and negative inclination angle) should be viewed as a zone without any change unless the boundary conditions cause a normal shock. Nevertheless, emission of Mach wave can occur in other situations. The approximation of weak weak wave with nonzero strength has engineering applicability in a very limited cases, especially in acoustic engineering, but for most cases it should be ignored. 14.2.2.3

Upstream Mach Number, M1 , and Shock Angle, θ

The solution for upstream Mach number, M1 , and shock angle, θ, are far much simpler and a unique solution exists. The deflection angle can be expressed as a function of these variables as δ For θ and M1   (k + 1) M1 2 cot δ = tan (θ) −1 2 (M1 2 sin2 θ − 1)

(14.51)

or tan δ =

2 cot θ(M1 2 sin2 θ − 1) 2 + M1 2 (k + 1 − 2 sin2 θ)

(14.52)

The pressure ratio can be expressed as Pressure Ratio P2 2 k M1 2 sin2 θ − (k − 1) = P1 k+1

(14.53)

The density ratio can be expressed as Density Ratio ρ2 U1n (k + 1) M1 2 sin2 θ = = ρ1 U2n (k − 1) M1 2 sin2 θ + 2

(14.54)

The temperature ratio expressed as

c2 2 T2 = 2 = T1 c1

Temperature Ratio

2 k M1 2 sin2 θ − (k − 1) (k − 1)M1 2 sin2 θ + 2 (k + 1) M1 2 sin2 θ

(14.55)

14.2. OBLIQUE SHOCK

597

The Mach number after the shock is Exit Mach Number M2 2 sin(θ − δ) =

(k − 1)M1 2 sin2 θ + 2 2 k M1 2 sin2 θ − (k − 1)

(14.56)

or explicitly M2 2 =

(k + 1)2 M1 4 sin2 θ − 4 (M1 2 sin2 θ − 1)(kM1 2 sin2 θ + 1)

2 k M1 2 sin2 θ − (k − 1) (k − 1) M1 2 sin2 θ + 2

(14.57)

The ratio of the total pressure can be expressed as

P02 P01

Stagnation Pressure Ratio k 1  k−1   k−1  k+1 (k + 1)M1 2 sin2 θ = (k − 1)M1 2 sin2 θ + 2 2kM1 2 sin2 θ − (k − 1)

(14.58)

Even though the solution for these variables, M1 and θ, is unique, the possible range deflection angle, δ, is limited. Examining equation (14.51) shows that the shock angle, θ , has to be in the range of sin−1 (1/M1 ) ≥ θ ≥ (π/2) (see Figureq14.8). The range

of given θ, upstream Mach number M1 , is limited between ∞ and 14.2.2.4

1/ sin2 θ.

Given Two Angles, δ and θ

It is sometimes useful to obtain a relationship where the two angles are known. The first upstream Mach number, M1 is Mach Number Angles Relationship M1 2 =

2 (cot θ + tan δ) sin 2θ − (tan δ) (k + cos 2θ)

(14.59)

The reduced pressure difference is

The reduced density is

2 (P2 − P1 ) 2 sin θ sin δ = 2 ρU cos(θ − δ)

(14.60)

ρ2 − ρ1 sin δ = ρ2 sin θ cos(θ − δ)

(14.61)

For a large upstream Mach number M1 and a small shock angle (yet not approaching zero), θ, the deflection angle, δ must also be small as well. Equation (14.51) can be simplified into k+1 θ∼ δ (14.62) = 2 The results are consistent with the initial assumption which shows that it was an appropriate assumption.

598

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

Defection angle

subsonic weak solution

1.0 < M1 < ∞ strong solution

θ min = sin−1

1 M1

supersonic weak soution

possible solution

no solution zone

θ, Shock angle θ=

π 2

θ max ∼

π

θ=0

2

Fig. -14.8. The possible range of solutions for different parameters for given upstream Mach numbers.

Fig. -14.9. Color-schlieren image of a two dimensional flow over a wedge. The total deflection angel (two sides) is 20◦ and upper and lower Mach angel are ∼ 28◦ and ∼ 30◦ , respectively. The image show the end–effects as it has thick (not sharp transition) compare to shock over a cone. The image was taken by Dr. Gary Settles at Gas Dynamics laboratory, Penn State University.

14.2. OBLIQUE SHOCK 14.2.2.5

599

Flow in a Semi–2D Shape

Example 14.2: In Figure 14.9 exhibits wedge in a supersonic flow with unknown Mach number. Examination of the Figure reveals that it is in angle of attack. 1) Calculate the Mach number assuming that the lower and the upper Mach angles are identical and equal to ∼ 30◦ each (no angle of attack). 2) Calculate the Mach number and angle of attack assuming that the pressure after the shock for the two oblique shocks is equal. 3) What kind are the shocks exhibits in the image? (strong, weak, unsteady) 4) (Open question) Is there possibility to estimate the air stagnation temperature from the information provided in the image. You can assume that specific heats, k is a monotonic increasing function of the temperature. Solution

Part (1) The Mach angle and deflection angle can be obtained from the Figure 14.9. With this data and either using equation (14.59) or potto-GDC results in M1

Mx

2.6810

2.3218

My s 0

My w 2.24

θs 0

θw 30

δ 10

P0 y P0 x

0.97172

The actual Mach number after the shock is then M2 =

M2n 0.76617 = = 0.839 sin (θ − δ) sin(30 − 10)

The flow after the shock is subsonic flow. Part (2) For the lower part shock angle of ∼ 28◦ the results are M1

Mx

2.9168

2.5754

My s 0

My w 2.437

θs 0

θw 28

δ 10

P0 y P0 x

0.96549

From the last table, it is clear that Mach number is between the two values of 2.9168 and 2.6810 and the pressure ratio is between 0.96549 and 0.97172. One of procedure to calculate the attack angle is such that pressure has to match by “guessing” the Mach number between the extreme values. Part (3) The shock must be weak shock because the shock angle is less than 60◦ . End Solution

600 14.2.2.6

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL Close and Far Views of the Oblique Shock

In many cases, the close proximity view provides a continuous turning of the deflection angle, δ. Yet, the far view shows a sharp transition. The traditional approach to reconcile these two views is by suggesting that the θ far view shock is a collection of many small weak shocks (see Figure 14.10). At the loδ cal view close to the wall, the oblique shock is a weak “weak oblique” shock. From the far view, the oblique shock is an accumulation of many small (or again weak) “weak shocks.” Fig. -14.10. A local and a far view of the oblique shock. However, these small “shocks” are built or accumulate into a large and abrupt change (shock). In this theory, the boundary layer (B.L.) does not enter into the calculation. In reality, the boundary layer increases the zone where a continuous flow exists. The boundary layer reduces the upstream flow velocity and therefore the shock does not exist at close proximity to the wall. In larger distance from the wall, the shock becomes possible. 14.2.2.7

Maximum Value of Oblique shock

The maximum values are summarized in the following Table .

Table -14.1. Table of maximum values of the oblique Shock k=1.4

Mx

My

δmax

θmax

1.1000

0.97131

1.5152

76.2762

1.2000

0.95049

3.9442

71.9555

1.3000

0.93629

6.6621

69.3645

1.4000

0.92683

9.4272

67.7023

1.5000

0.92165

12.1127

66.5676

1.6000

0.91941

14.6515

65.7972

1.7000

0.91871

17.0119

65.3066

1.8000

0.91997

19.1833

64.9668

1.9000

0.92224

21.1675

64.7532

2.0000

0.92478

22.9735

64.6465

2.2000

0.93083

26.1028

64.6074

14.2. OBLIQUE SHOCK

601

Table -14.1. Maximum values of oblique shock (continue) k=1.4

Mx

My

δmax

θmax

2.4000

0.93747

28.6814

64.6934

2.6000

0.94387

30.8137

64.8443

2.8000

0.94925

32.5875

65.0399

3.0000

0.95435

34.0734

65.2309

3.2000

0.95897

35.3275

65.4144

3.4000

0.96335

36.3934

65.5787

3.6000

0.96630

37.3059

65.7593

3.8000

0.96942

38.0922

65.9087

4.0000

0.97214

38.7739

66.0464

5.0000

0.98183

41.1177

66.5671

6.0000

0.98714

42.4398

66.9020

7.0000

0.99047

43.2546

67.1196

8.0000

0.99337

43.7908

67.2503

9.0000

0.99440

44.1619

67.3673

10.0000

0.99559

44.4290

67.4419

It must be noted that the calculations are for the perfect gas model. In some cases, this assumption might not be sufficient and different analysis is needed. Henderson and Menikoff15 suggested a procedure to calculate the maximum deflection angle for arbitrary equation of state16 . When the mathematical quantity D becomes positive, for large deflection angle, there isn’t a physical solution to an oblique shock. Since the flow “sees” the obstacle, the only possible reaction is by a normal shock which occurs at some distance from the body. This shock is referred to as the detach shock. The detached shock’s distance from the body is a complex analysis and should be left to graduate class and researchers in this area. 15 Henderson and Menikoff ”Triple Shock Entropy Theorem” Journal of Fluid Mechanics 366 (1998) pp. 179–210. 16 The effect of the equation of state on the maximum and other parameters at this state is unknown at this moment and there are more works underway.

602

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

θ δ

Fig. -14.11. Oblique shock occurs around a cone. This photo is courtesy of Dr. Grigory Toker, a Research Professor at Cuernavaco University of Mexico. According to his measurement, the cone half angle is 15◦ and the Mach number is 2.2.

14.2.2.8

Oblique Shock Examples

Example 14.3: Air flows at Mach number (M1 ) or Mx = 4 is approaching a wedge. What is the maximum wedge angle at which the oblique shock can occur? If the wedge angle is 20◦ , calculate the weak, the strong Mach numbers, and the respective shock angles. Solution The maximum wedge angle for (Mx = 4) D has to be equal to zero. The wedge angle that satisfies this requirement is by equation (14.28) (a side to the case proximity of δ = 0). The maximum values are: Mx

My

δmax

θmax

4.000

0.97234

38.7738

66.0407

To obtain the results of the weak and the strong solutions either utilize the equation (14.28) or the GDC which yields the following results Mx

My s

My w

θs

θw

δ

4.0000

0.48523

2.5686

1.4635

0.56660

0.34907

End Solution

Example 14.4: A cone shown in Figure 14.11 is exposed to supersonic flow and create an oblique shock. Is the shock shown in the photo weak or strong shock? Explain. Using the geometry

14.2. OBLIQUE SHOCK

603

Oblique Shock k=14 3

90 80

2.5 70 2

60

θ δ

My

50 1.5 40 1

30 20

0.5 10 0

0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Mx

Thu Jun 30 15:14:53 2005

Fig. -14.12. Maximum values of the properties in an oblique shock.

provided in the photo, predict at which Mach number was the photo taken based on the assumption that the cone is a wedge. Solution The measurements show that cone angle is 14.43◦ and the shock angle is 30.099◦ . With given two angles the solution can be obtained by utilizing equation (14.59) or the Potto-GDC.

M1 3.2318

My s

My w

θs

θw

δ

0.56543 2.4522 71.0143 30.0990 14.4300

P0 y P0 x

0.88737

Because the flow is around the cone it must be a weak shock. Even if the cone was a wedge, the shock would be weak because the maximum (transition to a strong shock) occurs at about 60◦ . Note that the Mach number is larger than the one predicted by the wedge. End Solution

604

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

α1 normal shock

α3 α2

oblique shock

Fig. -14.13. Two variations of inlet suction for supersonic flow.

14.2.3

Application of Oblique Shock

One of the practical applications of the oblique shock is the design of an inlet suction for a supersonic flow. It is suggested that a series of weak shocks should replace one normal shock to increase the efficiency (see Figure (14.13))17 . Clearly, with a proper design, the flow can be brought to a subsonic flow just below M = 1. In such a case, there is less entropy production (less pressure loss). To illustrate the design significance of the oblique shock, the following example is provided. Example 14.5: The Section described in Figure 14.13 and 14.14 air is flowing into a suction section at M = 2.0, P = 1.0[bar], and T = 17◦ C. Compare the different conditions in the two different configurations. Assume that only a weak shock occurs.

neglect the detached distance

α1 7◦ oblique sho ks 2 1

3

4

Normal shock

2

7◦

Solution Fig. -14.14.

Schematic for Example

The first configuration is of a normal shock for which the results18 are (14.5). Mx

My

Ty Tx

ρy ρx

Py Px

2.0000

0.57735

1.6875

2.6667

4.5000

P0y P0 x

0.72087

17 In fact, there is general proof that regardless to the equation of state (any kind of gas), the entropy is to be minimized through a series of oblique shocks rather than through a single normal shock. For details see Henderson and Menikoff “Triple Shock Entropy Theorem,” Journal of Fluid Mechanics 366, (1998) pp. 179–210. 18 The results in this example are obtained using the graphical interface of POTTO–GDC thus, no input explanation is given. In the past the input file was given but the graphical interface it is no longer needed.

14.2. OBLIQUE SHOCK

605

In the oblique shock, the first angle shown is Mx

My s

2.0000

My w

θs

θw

0.58974 1.7498 85.7021 36.2098

P0 y P0 x

δ 7.0000

0.99445

and the additional information by the minimal info in the Potto-GDC is Mx

My w

2.0000

δ

Py Px

Ty Tx

7.0000

1.2485

1.1931

θw

1.7498 36.2098

P0 y P0 x

0.99445

In the new region, the new angle is 7◦ + 7◦ with new upstream Mach number of Mx = 1.7498 resulting in Mx

My s

1.7498

My w

θs

θw

P0 y P0 x

δ

0.71761 1.2346 76.9831 51.5549 14.0000

0.96524

And the additional information is Mx

My w

1.7498

δ

Py Px

Ty Tx

7.0000

1.2626

1.1853

θw

1.5088 41.8770

P0 y P0 x

0.99549

An oblique shock is not possible and normal shock occurs. In such a case, the results are: Mx

My

Ty Tx

ρy ρx

Py Px

1.2346

0.82141

1.1497

1.4018

1.6116

P0 y P0x

0.98903

With two weak shock waves and a normal shock the total pressure loss is P04 P04 P03 P02 = = 0.98903 × 0.96524 × 0.99445 = 0.9496 P01 P03 P02 P01 The static pressure ratio for the second case is P4 P4 P3 P2 = = 1.6116 × 1.2626 × 1.285 = 2.6147 P1 P3 P2 P1 The loss in this case is much less than in a direct normal shock. In fact, the loss in the normal shock is above than 31% of the total pressure. End Solution

606

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

Example 14.6: A supersonic flow is approaching a very long two–dimensional bland wedge body and creates a detached shock at Mach 3.5 (see Figure 14.15). The half wedge angle is 10◦ . What is the requited “throat” area ratio to achieve acceleration from the subsonic region to the supersonic region assuming the flow is one–dimensional?

A∗

Fig. -14.15. Schematic for Example (14.6).

The detached shock is a normal shock and the results are My

Ty Tx

ρy ρx

3.5000

0.45115

3.3151

4.2609

10◦

My s

Solution

Mx

My w

P0y P0 x

Py Px

14.1250

0.21295

Now utilizing the isentropic relationship for k = 1.4 yields M

T T0

ρ ρ0

A A?

P P0

A×P A∗ ×P0

0.45115

0.96089

0.90506

1.4458

0.86966

1.2574

Thus the area ratio has to be 1.4458. Note that the pressure after the weak shock is irrelevant to the area ratio between the normal shock and the “throat” according to the standard nozzle analysis. End Solution

Example 14.7: The effects of a double wedge are explained in the government web site as shown in Figure 14.16. Adopt this description and assume that the turn of 6◦ is made of two equal angles of 3◦ (see Figure 14.16). Assume that there are no boundary layers and all the shocks are weak and straight. Perform the calculation for M1 = 3.0. Find the required angle of shock BE. Then, explain why this description has internal conflict.

D B

Slip Plane

P3 = P4

3 weak oblique shock or expension wave

weak oblique shock M1

1

0

4

C

E

2

A

Fig. -14.16. Schematic of two angles turn with two weak shocks.

Solution The shock BD is an oblique shock with a response to a total turn of 6◦ . The conditions for this shock are:

14.2. OBLIQUE SHOCK Mx

My s

3.0000

607 My w

θs

θw

0.48013 2.7008 87.8807 23.9356

P0 y P0 x

δ 6.0000

0.99105

The transition for shock AB is Mx

My s

3.0000

My w

θs

θw

0.47641 2.8482 88.9476 21.5990

P0 y P0 x

δ 3.0000

0.99879

For the shock BC the results are Mx

My s

2.8482

My w

θs

θw

0.48610 2.7049 88.8912 22.7080

P0 y P0 x

δ 3.0000

0.99894

And the isentropic relationships for M = 2.7049, 2.7008 are M

T T0

ρ ρ0

A A?

P P0

2.7049

0.40596

0.10500

3.1978

0.04263

0.13632

2.7008

0.40669

0.10548

3.1854

0.04290

0.13665

A×P A∗ ×P0

The combined shocks AB and BC provide the base of calculating the total pressure ratio at zone 3. The total pressure ratio at zone 2 is P02 P01 P02 = = 0.99894 × 0.99879 = 0.997731283 P00 P01 P00 On the other hand, the pressure at 4 has to be P4 P4 P04 = = 0.04290 × 0.99105 = 0.042516045 P01 P04 P01 The static pressure at zone 4 and zone 3 have to match according to the government suggestion hence, the angle for BE shock which cause this pressure ratio needs to be found. To do that, check whether the pressure at 2 is above or below or above the pressure (ratio) in zone 4. P02 P2 P2 = = 0.997731283 × 0.04263 = 0.042436789 P02 P00 P02 2 4 Since PP02 < PP01 a weak shock must occur to increase the static pressure (see Figure 13.13). The increase has to be

P3 /P2 = 0.042516045/0.042436789 = 1.001867743 To achieve this kind of pressure ratio the perpendicular component has to be

608

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL Mx

My

Ty Tx

ρy ρx

Py Px

1.0008

0.99920

1.0005

1.0013

1.0019

P0y P0 x

1.00000

The shock angle, θ can be calculated from θ = sin−1 1.0008/2.7049 = 21.715320879◦ The deflection angle for such shock angle with Mach number is Mx 2.7049

My s

My w

0.49525 2.7037

θs 0.0

θw 21.72

δ

P0y P0x

0.026233 1.00000

From the last calculation it is clear that the government proposed schematic of the double wedge is in conflict with the boundary condition. The flow in zone 3 will flow into the wall in about 2.7◦ . In reality the flow of double wedge will produce a curved shock surface with several zones. Only when the flow is far away from the double wedge, the flow behaves as only one theoretical angle of 6◦ exist. End Solution

Example 14.8: Calculate the flow deflection angle and other parameters downstream when the Mach angle is 34◦ and P1 = 3[bar], T1 = 27◦ C, and U1 = 1000m/sec. Assume k = 1.4 and R = 287J/KgK. Solution The Mach angle of 34◦ is below maximum deflection which means that it is a weak shock. Yet, the Upstream Mach number, M1 , has to be determined M1 = √

U1 1000 = 2.88 = 1.4 × 287 × 300 kRT

Using this Mach number and the Mach deflection in either using the Table or the figure or POTTO-GDC results in Mx 2.8800

My s

My w

0.48269 2.1280

θs 0.0

θw

δ

34.00

15.78

P0y P0x

0.89127

The relationship for the temperature and pressure can be obtained by using equation (14.15) and (14.13) or simply converting the M1 to perpendicular component. M1n = M1 sin θ = 2.88 sin(34.0) = 1.61 From the Table (??) or GDC the following can be obtained.

14.2. OBLIQUE SHOCK

609 P0 y P0x

Mx

My

Ty Tx

ρy ρx

Py Px

1.6100

0.66545

1.3949

2.0485

2.8575

0.89145

The temperature ratio combined upstream temperature yield T2 = 1.3949 × 300 ∼ 418.5K and the same for the pressure P2 = 2.8575 × 3 = 8.57[bar] And the velocity √ √ Un2 = My w k R T = 2.128 1.4 × 287 × 418.5 = 872.6[m/sec] End Solution

Example 14.9: For Mach number 2.5 and wedge with a total angle of 22◦ , calculate the ratio of the stagnation pressure. Solution Utilizing GDC for Mach number 2.5 and the angle of 11◦ results in Mx

My s

My w

θs

θw

δ

P0y P0 x

2.5000

0.53431

2.0443

85.0995

32.8124

11.0000

0.96873

End Solution

Example 14.10: What is the maximum pressure ratio that can be obtained on wedge when the gas is flowing in 2.5 Mach without any close boundaries? Would it make any difference if the wedge was flowing into the air? If so, what is the difference? Solution It has to be recognized that without any other boundary condition, the shock is weak shock. For a weak shock the maximum pressure ratio is obtained at the deflection point because it is closest to a normal shock. To obtain the maximum point for 2.5 Mach number, either use the Maximum Deflection Mach number’s equation or the Potto–GDC Mx

My max

θmax

δ

Py Px

Ty Tx

P0y P0x

2.5000

0.94021

64.7822

29.7974

4.3573

2.6854

0.60027

610

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

In these calculations, Maximum Deflection Mach’s equation was used to calculate the normal component of the upstream, then the Mach angle was calculated using the geometrical relationship of θ = sin−1 M1n /M1 . With these two quantities, utilizing equation (14.12) the deflection angle, δ, is obtained. End Solution

Example 14.11: 3

Consider the schematic shown in the following figure. Assume that the upstream Mach number is 4 and the deflection angle is δ = 15◦ . Compute the pressure ratio and the temperature ratio after the second shock (sometimes referred to as the reflective shock while the first shock is called the incidental shock).

2

stream line 1

θ

M1 = 4 δ

Fig. -14.17. (14.11).

Schematic for Example

Solution This kind of problem is essentially two wedges placed in a certain geometry. It is clear that the flow must be parallel to the wall. For the first shock, the upstream Mach number is known together with deflection angle. Utilizing the table or the Potto–GDC, the following can be obtained: Mx 4.0000

My s

My w

θs

θw

δ

0.46152 2.9290 85.5851 27.0629 15.0000

P0y P0x

0.80382

And the additional information by using minimal information ratio button in Potto–GDC is Mx 4.0000

My w

θw

δ

2.9290 27.0629 15.0000

Py Px

Ty Tx

1.7985

1.7344

P0y P0x

0.80382

With a Mach number of M = 2.929, the second deflection angle is also 15◦ . With these values the following can be obtained: Mx 2.9290

My s

My w

θs

θw

δ

0.51367 2.2028 84.2808 32.7822 15.0000

and the additional information is

P0y P0x

0.90041

14.2. OBLIQUE SHOCK Mx 2.9290

My w

611 θw

δ

2.2028 32.7822 15.0000

Py Px

Ty Tx

1.6695

1.5764

P0 y P0 x

0.90041

With the combined tables the ratios can be easily calculated. Note that hand calculations requires endless time looking up graphical representation of the solution. Utilizing the POTTO–GDC which provides a solution in just a few clicks. P1 P1 P2 = = 1.7985 × 1.6695 = 3.0026 P3 P2 P3 T1 T1 T2 = = 1.7344 × 1.5764 = 2.632 T3 T2 T3 End Solution

Example 14.12: A similar example as before but here Mach angle is 29◦ and Mach number is 2.85. Again calculate the downstream ratios after the second shock and the deflection angle. Solution Here the Mach number and the Mach angle are given. With these pieces of information by utilizing the Potto-GDC the following is obtained: Mx 2.8500

My s

My w

0.48469 2.3575

θs 0.0

θw

δ

29.00

10.51

P0 y P0 x

0.96263

and the additional information by utilizing the minimal info button in GDC provides Mx 2.8500

My w

θw

δ

2.3575 29.0000 10.5131

Py Px

Ty Tx

1.4089

1.3582

P0 y P0 x

0.96263

With the deflection angle of δ = 10.51 the so called reflective shock gives the following information Mx 2.3575

My s

My w

θs

θw

δ

0.54894 1.9419 84.9398 34.0590 10.5100

and the additional information of

P0 y P0 x

0.97569

612

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL Mx 2.3575

My w

θw

Py Px

Ty Tx

1.3984

1.3268

δ

1.9419 34.0590 10.5100

P0y P0x

0.97569

P1 P1 P2 = = 1.4089 × 1.3984 ∼ 1.97 P3 P2 P3 T1 T2 T1 = = 1.3582 × 1.3268 ∼ 1.8021 T3 T2 T3 End Solution

Example 14.13: Compare a direct normal shock to oblique shock with a normal shock. Where will the total pressure loss (entropy) be larger? Assume that upstream Mach number is 5 and the first oblique shock has Mach angle of 30◦ . What is the deflection angle in this case? Solution For the normal shock the results are Mx

My

Ty Tx

ρy ρx

Py Px

5.0000

0.41523

5.8000

5.0000

29.0000

P0y P0 x

0.06172

While the results for the oblique shock are Mx 5.0000

My s

My w

0.41523 3.0058

θs 0.0

θw

δ

30.00

20.17

Py Px

Ty Tx

2.6375

2.5141

P0y P0x

0.49901

And the additional information is Mx 5.0000

My w

θw

δ

3.0058 30.0000 20.1736

P0y P0x

0.49901

The normal shock that follows this oblique is Mx

My

Ty Tx

ρy ρx

3.0058

0.47485

2.6858

3.8625

Py Px

10.3740

P0y P0 x

0.32671

14.2. OBLIQUE SHOCK

613

The pressure ratios of the oblique shock with normal shock is the total shock in the second case. P1 P1 P2 = = 2.6375 × 10.374 ∼ 27.36 P3 P2 P3 T1 T1 T2 = = 2.5141 × 2.6858 ∼ 6.75 T3 T2 T3 Note the static pressure raised is less than the combination shocks as compared to the normal shock but the total pressure has the opposite result. End Solution

Example 14.14: C A flow in a tunnel ends up with two deδ2 θ2 stream line flection angles from both sides (see the D 1 4 following Figure 14.14). For upstream slip plane B Mach number of 5 and deflection angle 3 φ 0 of 12◦ and 15◦ , calculate the pressure 2 θ1 F at zones 3 and 4 based on the assumpstream line δ1 A tion that the slip plane is half of the difference between the two deflection angles. Based on these calculations, exIllustration for Example plain whether the slip angle is larger or Fig. -14.18. smaller than the difference of the de- (14.14). flection angle.

Solution The first two zones immediately after are computed using the same techniques that were developed and discussed earlier. For the first direction of 15◦ and Mach number =5. Mx 5.0000

My s

My w

θs

θw

δ

0.43914 3.5040 86.0739 24.3217 15.0000

P0 y P0 x

0.69317

And the additional conditions are Mx 5.0000

My w

θw

δ

3.5040 24.3217 15.0000

Py Px

Ty Tx

1.9791

1.9238

For the second direction of 12◦ and Mach number =5.

P0 y P0 x

0.69317

614

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL Mx 5.0000

My s

My w

θs

θw

δ

0.43016 3.8006 86.9122 21.2845 12.0000

P0y P0x

0.80600

And the additional conditions are Mx 5.0000

My w

θw

δ

3.8006 21.2845 12.0000

Py Px

Ty Tx

1.6963

1.6625

P0y P0x

0.80600

The conditions in zone 4 and zone 3 have two things that are equal. They are the pressure and the velocity direction. It has to be noticed that the velocity magnitudes in zone 3 and 4 do not have to be equal. This non–continuous velocity profile can occur in our model because it is assumed that fluid is non–viscous. If the two sides were equal because of symmetry the slip angle is also zero. It is to say, for the analysis, that only one deflection angle exist. For the two different deflection angles, the slip angle has two extreme cases. The first case is where match lower deflection angle and second is to match the higher deflection angle. In this case, it is assumed that the slip angle moves half of the angle to satisfy both of the deflection angles (first approximation). Under this assumption the conditions in zone 3 are solved by looking at the deflection angle of 12◦ + 1.5◦ = 13.5◦ which results in Mx 3.5040

My s

My w

θs

θw

δ

0.47413 2.6986 85.6819 27.6668 13.5000

P0y P0x

0.88496

with the additional information Mx 3.5040

My w

θw

δ

2.6986 27.6668 13.5000

Py Px

Ty Tx

1.6247

1.5656

P0y P0x

0.88496

And in zone 4 the conditions are due to deflection angle of 13.5◦ and Mach number 3.8006. Mx 3.8006

My s

My w

θs

θw

δ

0.46259 2.9035 85.9316 26.3226 13.5000

P0y P0x

0.86179

with the additional information Mx 3.8006

My w

θw

δ

2.9035 26.3226 13.5000

Py Px

Ty Tx

1.6577

1.6038

P0y P0x

0.86179

14.2. OBLIQUE SHOCK

615

From these tables the pressure ratio at zone 3 and 4 can be calculated P3 P3 P2 P0 P1 1 1 = = 1.6247 × 1.9791 ∼ 1.18192 P4 P2 P0 P1 P4 1.6963 1.6038 To reduce the pressure ratio the deflection angle has to be reduced (remember that at weak weak shock almost no pressure change). Thus, the pressure at zone 3 has to be reduced. To reduce the pressure the angle of slip plane has to increase from 1.5◦ to a larger number. End Solution

Example 14.15: The previous example gave rise to another question on the order of the deflection angles. Consider the same values as previous analysis, will the oblique shock with first angle of 15◦ and then 12◦ or opposite order make a difference (M = 5)? If not what order will make a bigger entropy production or pressure loss? (No general proof is needed). Solution Waiting for the solution End Solution

14.2.3.1

Retouch of Shock Drag or Wave Drag

Since it was established that the common stationary control volume explanation is erroneous and the steam lines are bending/changing direction when they touching the oblique shock (compare U1 6= 0 U1 = 0 ρ2 ρ1 with Figure (13.15)). The correct explaA A 1 2 moving nation is that increase of the momentum P2 object P1 into control volume is either requires increase of the force and/or results in accelstream lines eration of gas. So, what is the effects of the oblique shock on the Shock Drag? FigFig. -14.19. The diagram that explains the ure 14.19 exhibits schematic of the oblique shock drag effects of a moving shock considshock which show clearly that stream lines ering the oblique shock effects. are bended. There two main points that should be discussed in this context are the additional effects and infinite/final structure. The additional effects are the mass start to have a vertical component. The vertical component one hand increase the energy needed and thus increase need to move the body (larger shock drag) (note the there is a zero momentum net change for symmetrical bodies.). However, the oblique shock reduces the normal component that undergoes the shock and hence the total shock drag is reduced. The oblique shock creates a finite amount of drag (momentum and energy lost) while a normal shock as indirectly implied in the common explanation creates de facto situation where the shock grows to be infinite which of course impossible.

616

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

It should be noted that, oblique shock becomes less “oblique” and more parallel when other effects start to kick in.

14.3 Prandtl-Meyer Function 14.3.1

Introduction

m

ax

im

um

an

gl

e

Flow As discussed in Section 14.2 when the deflecdirection tion turns to the opposite direction of the flow, positive angle the flow accelerates to match the boundary condition. The transition, as opposed to the oblique shock, is smooth, without any jump in properties. Here because of the tradition, the deflection angle is denoted as a positive when it is away from the flow (see Figure 14.21). In a somewhat a similar concept to oblique shock there exists a “detachment” point above which Fig. -14.21. The definition of the angle for this model breaks and another model has to the Prandtl–Meyer function. be implemented. Yet, when this model breaks down, the flow becomes complicated, flow separation occurs, and no known simple model can describe the situation. As opposed to the oblique shock, there is no limitation for the Prandtl–Meyer function to approach zero. Yet, for very small angles, because of imperfections of the wall and the boundary layer, it has to be assumed to be insignificant. µ U Supersonic expansion and isentropic compression c M (Prandtl-Meyer function), are an extension of the Mach line 1 concept. The Mach line shows that a disturbance in a field µ p of supersonic flow moves in an angle of µ, which is defined M2 − 1 as (as shown in Figure 14.22)   Fig. -14.22. The angles of 1 µ = sin−1 (14.63) the Mach line triangle. M

or µ = tan−1 √

1 M1 − 1

(14.64)

A Mach line results because of a small disturbance in the wall contour. This Mach line is assumed to be a result of the positive angle. The reason that a “negative” angle is not applicable is that the coalescing of the small Mach wave which results in a shock wave. However, no shock is created from many small positive angles. The Mach line is the chief line in the analysis because of the wall contour shape information propagates along this line. Once the contour is changed, the flow direction will change to fit the wall. This direction change results in a change of the flow properties, and it is assumed here to be isotropic for a positive angle. This assumption,

14.3. PRANDTL-MEYER FUNCTION

617

θ -δ -Mach number relationship k = 1.4

60

1.05 1.10 1.15 1.20 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.5 5 6 7 8 9 10 15 800

55

50

45

δ, deflection angle

40

35

30

25

20

15

10

5

0

10

20

30

40

50

60

70

80

90

θ , shock angle

December 4, 2007 Fig. -14.20. The relationship between the shock wave angle, θ and deflection angle, δ, and Mach number for k=1.4. This figure was generate with GDC under command ./obliqueFigure 1.4. Variety of these figures can be found in the biggest gas tables in the world provided separately in Potto Project.

618

CHAPTER 14. COMPRESSIBLE FLOW 2–DIMENSIONAL

as it turns out, is close to reality. In this chapter, a discussion on the relationship between the flow properties and the flow direction is presented.

14.3.2

Geometrical Explanation x

dx=dU cos(90−µ)

M

ac

h

lin e

y U The change in the flow direction is assume to be Uy y+ Ux dU result of the change in the tangential component. y (90−µ) U U + d dν µ dy Hence, the total Mach number increases. Thereµ U fore, the Mach angle increase and result in a change in the direction of the flow. The velocity compo(U+dU) cos(dµ)−U nent in the direction of the Mach line is assumed to be constant to satisfy the assumption that the Fig. -14.23. The schematic of the change is a result of the contour only. Later, this turning flow. assumption will be examined. The typical simplifications for geometrical functions are used:

∼ sin(dν);

dν

(14.65)

cos(dν) ∼ 1 These simplifications are the core reasons why the change occurs only in the perpendicular direction (dν